POTASSIUM PERMANGANATE 1
duces an effective heterogeneous oxidant, has further expanded
Potassium Permanganate1-4
its usefulness.
The general features of the reactions of permanganate dissolved
KMnO4
in aqueous solutions, or in organic solvents with the aid of a phase-
transfer agent, and as a heterogeneous oxidant will be briefly de-
scribed, followed by specific examples.
[7722-64-7] KMnO4 (MW 158.04)
InChI = 1/K.Mn.4O/q+1;;;;;-1/rK.MnO4/c;2-1(3,4)5/q+1;-1
Aqueous Permanganate Oxidations. Potassium permanga-
InChIKey = VZJVWSHVAAUDKD-QPPHZJHPAS
nate is a general, but relatively nonselective, oxidant when used
in aqueous solutions. When an organic compound contains only
(oxidant; conversion of arenes into carboxylic acids,10,11
one site at which oxidation can readily occur, this reagent is a
Ä…-ketones,12-15 or Ä…-alcohols;14 degradation of aromatic rings;3
highly efficient and effective oxidant. For example, oleic acid is
preparation of diols,17,18 ketols,5,19,20,22 and Ä…-diketones22-24
converted into dihydroxystearic acid in quantitative yield when
from nonterminal alkenes; preparation of carboxylic acids,27
ć%
oxidized in a dilute aqueous solution of KMnO4 at 0 10 C.5
aldehydes26 and 1,2-diols28 from terminal alkenes; oxidation of
If the aqueous solution is made acidic by addition of mineral
alkynes to Ä…-diones;29,30 oxidation of enones to 1,4-diones;31
acid, the rate of reaction increases, most probably because of for-
conversion of 1,5-dienes into substituted tetrahydrofurans32,33 or
mation of permanganic acid1 which is known to be a very strong
lactones;34 conversion of primary and secondary alcohols into
oxidant.6 The rate of the reaction is also accelerated by addition
carboxylic acids1,2,37 and ketones,1-4,9,35 respectively; oxida-
of sodium or potassium hydroxide. It has been proposed that this
tion of allylic alcohols to Ä…,²-unsaturated ketones35 and other
acceleration may be due to ionization of the organic reductant; for
unsaturated alcohols and Ä…,É-diols to lactones;36,37 oxidation of
example, conversion of an alcohol into an alkoxide ion.1 How-
aliphatic thiols to disulfides and aromatic thiols to sulfonic acids;4
ever, similar observations for the oxidation of compounds such as
oxidation of sulfides and sulfoxides to sulfones,4,38-40 sulfinic
sulfides, which lack acidic hydrogens, suggests that other factors
acids to sulfonic acids,43 sulfites to sulfates,44 and thiones to
may be involved.7
ketones;45 preparation of tertiary nitroalkanes from the corres-
Under acidic conditions, permanganate is reduced to soluble
ponding amines;47 oxidation of tertiary amines to amides or
manganese(II) or -(III) salts, thus allowing for a relatively easy
lactams;48-50 allylic oxidations when used in conjunction with
workup. However, under basic conditions the reduction product
t-butyl hydroperoxide;51 preparation of iodoaromatic compounds
is a gelatinous solid, consisting primarily of manganese dioxide,
when used with I2 and sulfuric acid;52 oxidation of nucleic acids
that is difficult to separate from the product. As a consequence, for
to the corresponding diols and ketols;53 oxidation of guaiol and
laboratory scale preparations the reaction product is not isolated
related compounds to rearranged ketols;54 oxidation of poly(vinyl
until after the MnO2 has been reduced by addition of HCl and
alcohol) to poly(vinyl ketone);56 oxidation of nitroalkanes to
sodium bisulfite. For large scale (industrial) processes, MnO2 is
aldehydes or ketones; oxidation of imines to nitrones)
removed either by filtration or by centrifugation.
Alternate Name: potassium manganate(VII).
ć%
Physical Data: d 2.70 g cm-3; decomposition 237 C.
Phase-transfer Assisted Permanganate Oxidations.2
ć%
Solubility: water (at 20 C) 63.8 g L-1; sol acetone, methanol.
KMnO4 may be dissolved in nonpolar solvents such as benzene
Form Supplied in: purple solid; commercially available.
or CH2Cl2 by complexing the potassium ion with a crown ether
Handling, Storage, and Precautions: stable at or below rt.
or by replacing it with a quaternary ammonium or phosphonium
Because it is a strong oxidant it should be stored in glass, steel,
ion. Although most reactions observed are similar to those found
or polyethylene vessels. Sulfuric acid should never be added to
in aqueous solutions, the ability to dissolve permanganate in
permanganate or vice versa. Permanganate acid, an explosive
nonpolar solvents has greatly increased the range of compounds
compound, is formed under highly acidic conditions.
that can be oxidized.
The first example of a phase-transfer assisted permanganate
oxidation involved the complexing of the potassium ion by a crown
ether in benzene;8 however, it was later found that the use of
Original Commentary
quaternary ammonium or phosphonium salts was less expensive
Donald G. Lee and just as efficient.2
University of Regina, Regina, Saskatchewan, Canada Phase transfer into a nonpolar solvent can occur either from
an aqueous solution or from solid KMnO4. Evaluation of vari-
Introduction. Permanganate is an inexpensive oxidant that ous phase-transfer agents for these purposes has indicated that
has been widely used in organic syntheses. Its most common salt, benzyltributylammonium chloride is highly efficient for trans-
KMnO4, is soluble in water and as a consequence oxidations have fer from aqueous solutions while alkyltriphenylphosphonium
traditionally been carried out in aqueous solutions or in mixtures halides, tetrabutylammonium halides, and benzyltriethylammo-
of water and miscible organic solvents such as acetone, acetic acid, nium halides are all effective for the transfer from solid KMnO4.2
acetonitrile, benzonitrile, tributyl phosphate, or pyridine. The dis- Adogen 464, an inexpensive quaternary ammonium chloride com-
covery that KMnO4 can, with the aid of phase-transfer agents, mercially available, is usually satisfactory for both purposes.
be readily dissolved in nonpolar solvents such as CH2Cl2, and Quaternary ammonium and phosphonium permanganates can
the recent observation that is adsorption onto a solid support pro- also be used as stoichiometric oxidants. For descriptions of their
Avoid Skin Contact with All Reagents
2 POTASSIUM PERMANGANATE
O
properties, refer to the separate articles on Methyltriphenyl-
phosphonium Permanganate and Benzyltriethylammonium Per- KMnO4, alumina
(7)
manganate.
ClCH2CH2Cl, "
86%
Heterogeneous Permanganate Oxidations. The use of
OH
KMnO4, alumina
permanganate, activated by adsorption on a solid support, as a
(8)
heterogenous oxidant has further increased the scope of these re-
ClCH2CH2Cl, "
79%
actions. CH2Cl2 or 1,2-dichloroethane (if a high reflux tempera-
ture is required) are the preferred solvents and Alumina, silica, or
hydrated Copper(II) Sulfate are the most commonly used solid
Oxidation of Aromatic Rings. Permanganate will oxida-
supports. The selectivity of the oxidant is dramatically altered by
tively degrade aromatic rings under both acidic and basic
use of a solid support. For example, although carbon carbon dou-
conditions.3 The effect of acid and base on the reaction has been
ble bonds are very easily cleaved in homogeneous permanganate
demonstrated by the oxidation of 2-phenylpyridine; under basic
solutions, secondary allylic alcohols can be cleanly oxidized to
conditions the product is benzoic acid (presumably because the
the corresponding Ä…,²-unsaturated ketones without disruption of
oxidant attacks the site of greatest electron density) (eq 9), while
the double bond under heterogeneous conditions.9
under acidic conditions (where the nitrogen would be protonated)
In addition to increased selectivity, the use of permanganate
the product is picolinic acid (eq 10).3
under heterogeneous conditions allows for easy product isolation.
It is necessary only to remove spent oxidant by filtration followed
by flash evaporation or distillation of the solvent. Products iso- KMnO4
N
(9)
CO2H
lated in this way are often sufficiently pure to permit direct use in
OH
subsequent synthetic procedures.
Benzylic Oxidations. Permanganate oxidizes side chains of
H
KMnO4
aromatic compounds at the benzylic position.3 In aqueous solu-
NN
+ H+
+
tion, carboxylic acids are usually obtained (eqs 1 and 2).10,11
KMnO4
N CO2H
(1)
Me CO2H
H2O, py (10)
71%
MeO MeO
Polycyclic aromatic compounds are also oxidatively degraded
t-Bu t-Bu CO2H
KMnO4
(2) to a single-ring polycarboxylic acid (eq 11).16
CO2H
KMnO4
OH
The oxidation of alkylbenzenes proceeds through the corre-
sponding Ä…-ketones, which can occasionally be isolated (eqs 3
CO2H HO2C CO2H
and 4).12,13
+ (11)
CO2H HO2C CO2H
(3)
CO2H
O
Oxidation of Nonterminal Alkenes. Nonterminal alkenes
NN
can be converted into 1,2-diols, ketols, or diketones by choice
(4) of appropriate conditions. The reaction, which proceeds by syn
80%
addition of permanganate to the double bond as indicated, gives
O
the corresponding cis-diol under aqueous alkaline conditions
(eq 12).17
Under heterogeneous conditions where alumina (acid, Brock-
man, activity 1)14 or copper sulfate pentahydrate15 is used as the
OH
O
O
solid support, Ä…-ketones and alcohols are obtained with little or
+ MnO4
Mn
O
no carbon carbon cleavage (eqs 5 8).
O H2O
45%
KMnO4, alumina
(5)
ClCH2CH2Cl, "
OH
69% O (12)
OH
KMnO4, CuSO4" 5H2O
Syn addition can also be achieved in nonaqueous solvents with
(6)
the aid of a phase-transfer agent (PTA). Subsequent treatment with
CH2Cl2
88% O
aqueous base gives 1,2-diols in good yields2 (eq 13).18 Equally
A list of General Abbreviations appears on the front Endpapers
POTASSIUM PERMANGANATE 3
good results were reported when the reaction was carried out in of the Lemieux von Rudloff reagent (aqueous potassium perio-
aqueous t-butyl alcohol.18 date containing catalytic amounts of permanganate).3,25 Under
heterogeneous conditions, either aldehydes or carboxylic acids
OH
1. KMnO4, PTA, CH2Cl2
are obtained, depending on the conditions used (eqs 20 and 21).26
(13)
2. 10% NaOH
OH
O
86%
KMnO4, alumina, H2O
H
(20)
H
CH2Cl2
Under neutral conditions the product obtained from the oxi-
O
75%
dation of alkenes is the corresponding ketol.5 Good yields are
obtained when aqueous acetone containing a small amount of
KMnO4, silica
CO2H
acetic acid (2 5%) is used as the solvent. The function of acetic
(21)
HO2C
C6H6
acid is to neutralize hydroxide ions produced during the reduc-
74%
tion of permanganate. The oxidations of 5-decene and methyl
2-methylcrotonate provide typical examples (eqs 14 and 15).19,20
KMnO4
Oxidation of Terminal Alkenes. Although oxidation of ter-
minal alkenes by permanganate usually results in cleavage of the
MeCOMe, H2O, MeCO2H
74% carbon carbon double bond to give either a carboxylic acid27 or
an aldehyde,26 1,2-diols can be obtained through use of a phase-
OH
transfer assisted reaction (eqs 22 24).2,28
(14)
KMnO4, PTA
O
CO2H
( )17 (22)
( )17
CH2Cl2, H2O
O O
75%
KMnO4
CO2Me
(15)
OMe
KMnO4, alumina, H2O
MeCOMe, H2O, H+
CHO
OH
(23)
80% ( )12 ( )12
CH2Cl2
55%
Heterogeneous oxidations of alkenes with a small amount of t-
butyl alcohol and water present to provide an  omega phase 21
OH
1. KMnO4, CH2Cl2, PTA
results in the formation of Ä…-ketols in modest to good yields
( )5
( )5 OH (24)
2. 3% NaOH
(eqs 16 and 17).22
80%
O
OH
KMnO4, CuSO4" 5H2O
(16)
Oxidation of Alkynes. Oxidation of nonterminal alkynes
CH2Cl2, t-BuOH, H2O
results in the formation of Ä…-diones. Good yields are obtained
55%
when aqueous acetone containing NaHCO3 and MgSO4,29 or
O
CH2Cl2 containing about 5% acetic acid,30 is used as the solvent
O O
KMnO4, CuSO4" 5H2O
(eqs 25 27). A phase-transfer agent to assist in dissolving KMnO4
CH2Cl2, t-BuOH, H2O
must be used when CH2Cl2 is the solvent. Terminal alkynes are
79% OH
oxidatively cleaved, yielding carboxylic acids containing one
(17)
carbon less than the parent alkyne.
Under anhydrous conditions, 1,2-diones are formed in good
KMnO4, PTA
yields when alkenes are oxidized by permanganate. Appropriate (25)
( )3 CH2Cl2, AcOH ( )3CO2H
conditions can be achieved by using acetic anhydride solutions
61%
(eq 18)23 or by dissolving permanganate in CH2Cl2 with the aid
of a phase-transfer agent (eq 19).24
O
KMnO4, PTA
(26)
O
KMnO4 CH2Cl2, AcOH
O
(18)
80%
Ac2O
O
66%
O
KMnO4, acetone, H2O
(27)
O
6
KMnO4, PTA
NaHCO3, MgSO4 6 6
(19) 6
O
81%
CH2Cl2, MeCO2H, H2O
O
69%
Similar yields are obtained under heterogeneous conditions, Oxidation of Enones to 1,4-Diones. Enones react with
where workup procedures are much easier.22 nitroalkanes (Michael addition) to form Å‚-nitro ketones that can
The carbon carbon double bonds of alkenes can also be be oxidized in good yield to 1,4-diones under heterogeneous con-
oxidatively cleaved to give carboxylic acids in good yield by use ditions (eq 28).31
Avoid Skin Contact with All Reagents
4 POTASSIUM PERMANGANATE
OO OH O
F KMnO4, silica
KMnO4, CuSO4" 5H2O
+ MeCH2NO2
(34)
( )4 ( )4
MeCN C6H6
CH2Cl2
89%
NO2 80%
O
(28)
KMnO4, CuSO4" 5H2O
O
CH2Cl2
HO
no product (35)
Oxidation of 1,5-Dienes. The oxidation of 1,5-dienes results
in the formation of 2,5-bis(hydroxymethyl)tetrahydrofurans with KMnO4, CuSO4" 5H2O
(36)
O
the indicated stereochemistry (eq 29).32 When R6 in (eq 29) is
CH2Cl2, H2O
O
OH
chiral, a nonracemic product is obtained.33 Use of heterogeneous
56%
conditions results in the formation of lactones (eq 30).34
Good yields of carboxylic acids are obtained from primary
KMnO4, CO2
alcohols under heterogeneous conditions (KMnO4/CuSO4·5H2O)
R1 R6 MeCOMe, H2O R3
R4
only when a base such as KOH or Cu(OH)2·CuCO3 is intermixed
R6 (29)
R1 O
R2 R3 R4 R5  20 °C with the solid support.37 Under these conditions the reagent has
R2 R5
60 70%
OH HO
also been reported to be selective for primary alcohols.37
The oxidation of Ä…,É-diols under heterogenous conditions
H
KMnO4, CuSO4" 5H2O
results in the formation of lactones. A good example is found
CH2Cl2
CH2OAc
H in the preparation of 3-hydroxy-p-menthan-10-oic acid lactone
(eq 37).37
OAc
OH
O
+ (30)
O
OAc
O O
O KMnO4, CuSO4" 5H2O
(37)
62% 8%
HO
O
CH2Cl2
83%
HO
O
Oxidation of Alcohols and Diols. Primary and secondary
alcohols are converted to carboxylic acids and ketones, respec-
tively, when oxidized by aqueous permanganate under either
Oxidation of Organic Sulfur Compounds. Aromatic thiols
acidic or basic conditions (eq 31).1 Similar results are obtained
are oxidized by permanganate to the corresponding sulfonic acids
with phase-transfer assisted oxidations in organic solvents such
while aliphatic thiols usually give disulfides, which are resistant
as CH2Cl2 (eq 32).2
to further oxidation.4 Sulfides and sulfoxides are easily oxidized
in CH2Cl2 to the corresponding sulfones under both homoge-
KMnO4
neous38,39 and heterogeneous conditions (eqs 38 42).40
( )4 OH H2O, H2SO4 ( )4CO2H (31)
SH SO3
66%
KMnO4
N N
(38)
OH , H2O
N O N O
KMnO4, Adogen
91%
(32)
Me Me
CH2Cl2, AcOH
OH O
92%
KMnO4, PTA
(39)
SS
CH2Cl2, H2O
O
Heterogeneous oxidations are very effective with secondary 90% O
alcohols (eq 33)35 and provide the added advantage that al-
O
O
lylic secondary alcohols can be converted to the corresponding
S S
KMnO4, PTA
Ä…,²-unsaturated ketones without disruption of the double bond
(40)
(eq 34).9 Unsaturated secondary alcohols in which the double CH2Cl2, H2O
O O
91%
bond is not adjacent to the carbon bearing the hydroxy group are
resistant to oxidation (eq 35) unless an  omega phase 21 is created
KMnO4, PTA
(41)
Bu2SO Bu2SO2
by adding a small amount of water (50 µL per g KMnO4). The
CH2Cl2, H2O
products are lactones under these conditions (eq 36).36
86%
OH O
O O
KMnO4, CuSO4" 5H2O S KMnO4, CuSO4" 5H2O
(33) S (42)
( )7 ( )7
CH2Cl2 CH2Cl2
100% 96%
A list of General Abbreviations appears on the front Endpapers
POTASSIUM PERMANGANATE 5
NH2 KMnO4 O
Permanganate oxidizes sulfoxides more readily than sulfides,
(50)
as indicated by the products obtained from the oxidation of com-
t-BuOH, H2O
70%
pounds containing both sulfide and sulfoxide functional groups
(eqs 43 and 44).41,42
Amides (or lactams, if the amine is cyclic) are obtained from
O the oxidation of tertiary amines (eqs 51 and 52).48-50
O O
KMnO4
(43)
MeS S MeS S
Me Me
Et Et
MeCOMe, H2O
97% KMnO4
N N O
(51)
MeCOMe, AcOH
S S
70%
QMnO4
(44)
S S
CH2Cl2 F F
O
O O KMnO4
O
F F
Q = benzyltriethylammonium ion
N N
MeCOMe
(52)
70%
N N
The greater ease of oxidation of sulfoxides is also responsible
for the observation that gem-disulfides are oxidized to monosul-
fones.42 Monosulfoxides, although not isolated, are likely to be
Miscellaneous Oxidations. Use of permanganate in conjunc-
intermediates in these reactions (eq 45).
tion with tert-Butyl Hydroperoxide results in allylic oxidation
(eq 53).51
O O
KMnO4 O
KMnO4
MeS SMe
MeS S
MeS S
R R
Me
MeCOMe
Me
(45)
70%
KMnO4, t-BuOOH
Oxidation of sulfinic acids results in the formation of sulfonic C6H6, silica (53)
acids,43 while sulfites give sulfates (eqs 46 and 47).44
AcO AcO O
SO2H SO3
KMnO4
Aromatic compounds are oxidized to aryl iodides when treated
(46)
with permanganate, Iodine, and Sulfuric Acid (eq 54).52
OH , H2O
( )11 ( )11
70%
KMnO4, I2
(54)
I
O O
KMnO4
O H2SO4
(47)
S O S
70%
O
AcOH
O O
45%
Chemical modification of nucleic acids by treatment with
permanganate results in oxidation of the 5 double bond to give
Cyclic thiones are readily oxidized to the corresponding
either diols or ketols (eq 55).53
ketones by permanganate (eq 48).45
O
S
S
KMnO4
KMnO4
HN OH
MeO OMe
O pH 8.6
MeCOMe
O N OH
36%
64%
R
HN
(55)
O O
O N
S
KMnO4
R HN OH
MeO OMe (48)
pH 4.3
O N O
40%
R
Oxidation of Amines. The synthetic usefulness of perman-
Guaiol and related compounds can be oxidized to rearranged
ganate as an oxidant for aliphatic amines is decreased by the fact
ketols using aqueous glyme as the solvent (eq 56).54
that a complex mixture of products is often obtained.4,46 Good
yields of tertiary nitroalkanes can, however, be obtained from the
HO
oxidation of the corresponding amines (eq 49).47
KMnO4, pH 8
(56)
KMnO4 glyme, H2O
(49) 70%
R3CNH2 R3CNO2
OH
O
MeCOMe, H2O
OH
70 80%
Primary and secondary amines react with permanganate in cis-2,5-Dihydro-2,5-dimethoxyfuran is oxidized to the corre-
buffered, aqueous t-butyl alcohol to give aldehydes and ketones sponding Ä…-diol in preference to the trans compound (eqs 57
(eq 50).46 and 58).55
Avoid Skin Contact with All Reagents
6 POTASSIUM PERMANGANATE
MeO OMe MeO OMe
KMnO4 NO2 NaH NO2
O O KMnO4
(57)
THF, H2O
t-BuOH H2O
HO OH
O
fast
(63)
MeO MeO
KMnO4
O O
(58)
THF, H2O
91%
OMe OMe
HO OH
slow O
NaH KMnO4
( )8 NO2 ( )8 NO2 ( )8 H (64)
Oxidation of poly(vinyl alcohol) by permanganate results in the t-BuOH H2O
59%
formation of poly(vinyl ketone) (eq 59).56
OH O
KMnO4
Nitrones can be obtained from the oxidation of imines by
(59)
KMnO4 in a two-phase CH2Cl2/H2O solution containing a
n n
phase-transfer agent (PTA) such as tetrabutylammonium chloride
(eq 65).61
Treatment of 5-unsaturated steroids with KMnO4/CuSO4·
5H2O in CH2Cl2 containing catalytic amounts of t-butyl
N t-Bu
KMnO4, PTA
alcohol and water results in formation of the corresponding 5²,6²-
epoxide (eq 60).22,57
CH2Cl2, H2O

O
+
N t-Bu HN t-Bu
KMnO4, CuSO4" 5H2O
+ (65)
O
CH2Cl2, t-BuOH, H2O
92%
89% 11%
AcO
(60)
First Update
AcO
O
María Ribagorda & Javier Adrio
Universidad Autónoma de Madrid, Madrid, Spain
The oxidation of 7-cholesterol acetate by KMnO4 under
neutral or slightly basic conditions results in formation of all-
Benzylic and Allylic Oxidations. Aliphatic side chains of
cis-epoxydiol (eq 61).58
aromatic compounds are oxidized at the benzylic position in the
presence of potassium permanganate, whereas carboxylic acids
were obtained when KMnO4 was used in aqueous solutions.
Higher selectivity was observed when the reaction was performed
KMnO4
under heterogeneous conditions, giving rise to the ketones and
H2O
alcohols with little or no overoxidation. Hence, using perman-
ganate adsorbed on moist alumina, or copper sulfate pentahydrate,
AcO
excellent yields and selectivities were obtained in the alkylben-
zene aliphatic side chain. The reaction can be carried out under
62
very mild, neutral conditions (eq 66).
(61)
O
O
AcO
HO
OH
KMnO4/CuSO4Å"5H2O
(66)
CH2Cl2, 72 h, 95%
Aliphatic nitro compounds are converted into the correspond-
ing oxo compounds on treatment with basic permanganate.59,60
The use of ultrasonic irradiation permits shorter reaction times
Because these reactions are carried out under basic conditions, it
in the heterogeneous oxidation with KMnO4/CuSO4·5H2O at
is likely that anions are intermediates, as suggested in eqs 62 64.
room temperature. Significantly higher yields were accomplished
KMnO4 O
OH
in sonochemical experiments than in similar silent experiments
(62)
NO2
NO2
(eq 67).63 Solvent-free conditions have also been reported using
H2O
H
83 97%
the copper sulfate pentahydrate solid support.64
A list of General Abbreviations appears on the front Endpapers
POTASSIUM PERMANGANATE 7
O
temperature, the oxidation process became selective, affording
KMnO4/CuSO4Å"5H2O 3,4-dihydroisoquinolines in preparative yields (eq 72).70
(67)
O O
MeO
)))), 93%
KMnO4, 18-crown-6
CH2Cl2, rt, 2 h
silent, 17%
NH CH2Cl2, 20 min
MeO
solvent-free, 5 min, 95%
75%
Ph
Permanganate supported on active manganese dioxide can be MeO
used effectively under solvent-free conditions for the oxidation of
(72)
N
alkylarenes (eq 68). The residue that remains after the extraction
MeO
of organic compounds, manganese dioxide, can be recycled.65
Ph
O
1,2-Dihydro-[2,7]naphthyridines can be easily oxidized into the
KMnO4/MnO2
respective naphthyridine-1-ones derivatives in good yields with
(68)
solvent-free, 23 h
potassium permanganate in the presence of 18-crown-6 at room
89%
temperature (eq 73).71
The combination of potassium permanganate and an ion R2
KMnO4, 18-crown-6
NN
exchange resin (IER) has been described as an efficient ox-
CH2Cl2, 2 h
CO2Me
idant system for alkylarenes under heterogeneous conditions
61 92%
(eq 69).66,67
CO2Me
O
O
R2
KMnO4/IER
NN
(73)
(69)
CH2Cl2, reflux, 5.30 h
CO2Me
86 91%
CO2Me
Alkyl arenes are oxidized to the corresponding Ä…-ketones in
Using potassium permanganate under basic conditions, the
moderate to good yields under heterogeneous conditions without
10-position of the 4,5-epoxymorphinan can be oxidized in good
the use of solid supports using acetonitrile as the solvent at room
temperature (eq 70). No reaction was observed whenR=H.68 yield. The reaction can be performed on a large scale (eq 74).72
The oxidation of toluene using aqueous potassium perman-
ganate was studied in the presence of acoustic or hydrodynamic
O
cavitation (eq 75). The reaction was found to be considerably
KMnO4
R R
(70) accelerated at ambient temperature in the presence of cavitation.
CH3CN, rt, 15 30 h
About six times more product would be obtained in the case of
58 80%
hydrodynamic cavitation than in the case of acoustic (ultrasound)
R = Alkyl, Ar
cavitations at the same energy dissipation.73
O
Convenient syntheses of 7-halo-1-indanones and 8-halo-1-
tetralones have been reported through regioselective oxidation of
N
4-amidoindans with potassium permanganate (eq 71).69
OAc
KMnO4, MgSO4 aq
NaOH, tBuOH, rt
NH2
27 h, 74%
1. Ac2O, EtOH
O
2. KMnO4, acetone
MeO
OAc
H2O, MgSO4, 0 °C, 16 h
O
n
O N
NHAc X
O O
OAc
(74)
(71)
n n
O
overall yield X = halogen
MeO
OAc
n = 1, 70%
CO2H
n = 2, 66%
KMnO4 aq
(75)
The oxidation of 1,2,3,4-tetrahydroquinolines with potassium
hydrodynamic cavitation
permanganate in acetone at room temperature is a fast exother-
3 h, 44%
mic reaction leading to the corresponding isoquinoline. How-
ever, when the reaction is carried out in the presence of a Allylic oxidations also can be achieved using potassium
catalytic amount of 18-crown-6 in a CH2Cl2 solution at room permanganate. Thus, tetrahydropyridines undergo the introduc-
Avoid Skin Contact with All Reagents
8 POTASSIUM PERMANGANATE
R
tion of an oxo group into the allyl position of the piperidine frag-
ment (eq 76).74 Successive permanganate oxidations of the allyllic
KMnO4/solid support
carbon atoms in the piperidine ring can be achieved to afford 1-
CH2Cl2, 0.3-16 h
aminoalkan-3-ones.75
89-92%
AcO
R
Ph
Ph
KMnO4, CH3CN
(76)
(80)
rt, 50 min
N O
N
65%
Me
Me
AcO
O
The oxidation of cholesteryl acetate can be achieved as well
with potassium permanganate in the presence of a Lewis acid,
Oxidations of Alkenes. Benzaldehydes can be prepared in
either FeCl3 or ZnCl2, to afford the corresponding epoxides in
good yields from the oxidative cleavage of styrene and cinnamic
very good yields (eq 81).79,80
acid derivatives by permanganate oxidation under heterogeneous
conditions. Alumina and Amberlite IR-120 can be used as solid
supports with equally good results (eq 77).76
KMnO4/FeCl3
O
KMnO4/solid support acetone, 14 h
(77)
80%
CH2Cl2, overnight
H
AcO
90%
Rapid and efficient oxidative cleavages of olefins with potas-
(81)
sium permanganate in the presence of solid polymeric cation
exchange resins in good yield have been reported (eq 78).67
AcO
O
KMnO4, tulsion T42
The highly selective dihydroxylation of 2-spirotanic olefins
(78)
t
O
BuOH, CH2Cl2, rt
bearing ketone-, Ä…-ketol-, epoxy-, hydroxyl-, and acetoxy func-
3 h, 82% H
tions can be achieved using homogeneous nonaqueous potassium
permanganate (eq 82).81
Ultrasound accelerates permanganate oxidations of olefins to
cis-1,2-diols in aqueous media under neutral conditions (eq 83).82
The potassium permanganate oxidation of the side chain at
C(9) of some labdanic diterpenoids leads to intermediates that
O
R
have been transformed into Ambrox©-like compounds (flavor
KMnO4/Et3BnN+Cl-
compounds). The exocyclic double bond at C(8) remains unal-
O
tered under the oxidizing conditions. While a mixture of triols [at
CH2Cl2, 90 min
67%
C(3 ),C(4 ), C(5 )] and the methyl ketone were obtained using 1.5
equiv of oxidant, the latter compound could be obtained in good
HO
yields using 3 equiv of potassium permanganate (eq 79).77
O
O
OH
O
O
HO (82)
KMnO4 (3 equiv)
(79)
HO
CH2Cl2, 0 ºC, 14 h
HO
68%
O
H
H
OH
OH
OH
R1 R2 KMnO4/t-BuOH/H2O R1 R2 (83)
n
n
))), 5-20 min
Permanganate oxidation under heterogeneous conditions has
OH
n = 0, 1 55-88%
also been applied to the epoxidation of 5 steroids. The epoxi-
dation takes place from the more hindered side of the molecule.
R1 = H, C6H5, 4-MeC6H4, 4-MeOC6H4
The best results were achieved with KMnO4/Fe2(SO4)3·nH2O
R2 = H, Br
(eq 80).78
A list of General Abbreviations appears on the front Endpapers
POTASSIUM PERMANGANATE 9
Pr Pr
The utilization of potassium permanganate in combination with
18-crown-6 provides a versatile procedure for the dihydroxylation
Ph
of lactams (eq 84).83
N
N
N
Pr
KMnO4
N R
OH N
Zn N
CH2Cl2, 20 °C, 45 min
OH
EtO2C EtO2C
R
92%
N
Pr
KMnO4, 18-crown-6
N
N
N
(84)
N N
CH2Cl2, pH 9, 3 h Ph
O O
O O
31%
Pr Pr
Ph Ph
Pr Pr
An asymmetric phase transfer dihydroxylation of enones using
Ph
O
potassium permanganate and a chiral quaternary ammonium salt
N
N
N
Pr
have been recently described.84 Moderate to good enantioselec-
N R
tivities were achieved, although large quantities of catalyst are
N (88)
Zn N
required (eq 85).
R
N
Pr
N
N
N
O
OH
Bu Bu Ph
KMnO4, AcOH
(85)
Ph Ph
Pr Pr
CH2Cl2, -30 °C, 7 h
HO
O O
Br
CO2Et
CO2Et
41%, 63% ee KMnO4-Al2O3
N (89)
acetone, 0°C, 2 h
BnO
CO2Et
70% CO2Et
The oxidative cyclization of 1,5-dienes was elegantly used by
N
Kociénski and co-workers as a key step in the synthesis of the
C(21) C(30) (salinomycin numbering) lactone fragment of Sali-
Potassium permanganate supported on zeolite can be used for
nomycin. The success of the oxidation lies in the control of pH.
the selective oxidative cleavage of various enamines to the corre-
Use of acetate buffer mixed with acetic acid at pH 5 gave complex
ć%
sponding ketones in good yields (eq 86).85
mixtures, but the same reaction conducted at pH 6 and at -35 C
was quite clean, giving the desired oxidative cyclization product
O
together with a diastereoisomer (dr 6:1) in 54% yield (eq 90).90
KMnO4/zeolite
cis-Solamin and its diastereomer have been also synthesized
N O (86)
1,2-dichloroethane, rt, 6 h
using the permanganate-promoted oxidative cyclization of 1,5-
C9H19
94%
dienes to create the tetrahydrofuran diol core (eq 91).91,92
C9H19
H
Oxidation of enamines can also be performed with potassium
H
OH O
O
permanganate supported on neutral alumina. This reagent system
OH
HO2C
21 O
allows the selective oxidation of enamine carbon-carbon double OO
O
H H H
bonds in the presence of distal alkenes (eq 87).86
OH
30
O
Salinomycin
KMnO4/Al2O3 H
21
OH
N
acetone, rt, 4 h
O
O
92%
O
30
(87)
O
O
O
O
O
4,5-Diamino-porphirazine systems undergo oxidation with
KMnO4
ć%
potassium permanganate at 20 C to give rise to the corresponding
pH 6 acetate buffer
sec-porphyrazines. These were shown to be efficient sensitizers for
HO
AcOH, acetone, H2O
the production of singlet oxygen (eq 88).87,88
Et
(90)
-35 °C, 5 h, 54%
O
Et
Oxidation of Dienes and Trienes. Potassium permanganate
O
O
HO
adsorbed on alumina has been used to oxidize 1,4-cyclohexadienes
to the corresponding aromatic compounds. These heterogeneous N
N
reactions are an efficient alternative to the synthesis of highly SO2
SO2
substituted aromatic systems (eq 89).89
Avoid Skin Contact with All Reagents
10 POTASSIUM PERMANGANATE
KMnO4, AcOH
KMnO4, AcOH
Adogen 464, EtAc
Adogen 464, EtOAc
N N
-60 °C, 20%
O O
-30 to 0 °C, 55%
S S
10
O (10:1) O
O O
O
O
(94)
O
N
H H
O
N
10
OH OH
S
H H
O
OH OH
S
O
O
O
+
Oxidation of Alkynes. Permanganate oxidation is one of the
O
most attractive methods for the synthesis of 1,2-diketones due
(91)
O
N to the availability of starting materials and the ease of work up.
10
H H
OH OH
Recently, this method has been extended to alkynes substituted
S
O
O with heterocycles such as pyridine or thiophene (eq 95).97
O
KMnO4
Promising levels of induction have been achieved in the asym-
R
(95)
R
metric phase-transfer-catalyzed oxidative cyclization of 1,5-dien- rt, 4 h
(55 96%) O
ones by permanganate using a chiral ammonium salt (eq 92).93
S
KMnO4, AcOH
, , ,
N
,
R =
S
Ar
CH2Cl2, -30 °C N
N
O
C6H13
Br
N
Ä…-Keto esters and derivatives can be easily prepared through
BnO
potassium permanganate oxidation of the corresponding substi-
tuted alkynyl ethers. The reaction was accomplished with a great
variety of substrates containing different functionality (eq 96).98
N
O
O
R OKMnO4, pH = 7 O
(96)
R
Ar (92)
O 2-5 min, 76-98%
HO
H H
O
OH
Ar = Ph (47%, 58% ee)
An alternative method for the preparation of Ä…-keto esters from
Ar = p-FC6H4 (50%, 72% ee) terminal alkynes via bromination and permanganate oxidation has
been recently reported (eq 97).99
Ar = p-BrC6H4 (26%, 75% ee)
KMnO4, NaHCO3, MgSO4
Br
The permanganate oxidation of 1,5,9-trienes took place regio-
MeOH:H2O 1:1
selectively to afford substituted octahydro-2,2 -bifuranyl systems 93%
(eq 93).94,95
O
(97)
OMe
CO2Me
KMnO4, AcOH
O
acetone, acetate buffer
(pH 6.5)
52%
Oxidation of Organic Alcohols and Diols. The classical
oxidation of primary alkyl or benzyl alcohols with potassium
OH
permanganate has been supplemented by a new technique invol-
O
HO
(93)
O H
ving solid supports, such as Montmorillonite K-10,100 alumina
CO2Me
silicate,101 Kieselguhr,102 zirconyl chloride octahydrate,103 cop-
HO
per sulfate pentahydrate,63 or silica sulfuric acid-wet silica104
to render the corresponding aldehydes without concomitant
1,6-Dienes also undergo permanganate oxidative cyclizations, oxidation to carboxylic acids. Some examples of the oxidation
affording only the cis-isomers. Good levels of asymmetric of benzyl alcohol with supported potassium permanganate in
induction have been achieved using a sultam as a chiral auxiliary heterogeneous or solvent-free conditions are shown in eq 98,
(eq 94).96 Table 1.
A list of General Abbreviations appears on the front Endpapers
POTASSIUM PERMANGANATE 11
Table 1
Entry Conditions Solvent T Time Yield (%)
1 KMnO4/K10 solvent-free rt 2 h 79
ć%
2 KMnO4/aluminum silicate toluene 70 80 C 30 min 97
3 KMnO4/Kieselguhr solvent-free rt 30 min 98
4 KMnO4/ZrOCl2·8H2OEt2O rt 3.5 h 95
5KMnO4/CuSO4·5H2O, ))) CH2Cl2 rt 1.5 h 80
6 KMnO4/SiO2-OSO3H, wet SiO2 CH2Cl2 reflux 30 min 95
1,3-Dialkylimidazolium salts comprise an important class of
O
ionic liquids and have been of considerable interest as being
OH supported-KMnO4 H
environmentally benign. They have been employed as a reaction
(98)
media in the oxidation of different benzylic alcohols to the corres-
ponding carbonyl compounds with potassium permanganate
(eq 103).105 Primary and secondary aliphatic alcohols, however,
These solid-supported permanganate conditions have also been
required longer reaction times and higher temperatures. Again,
used to oxidize secondary alcohols to the corresponding ketones.
For example, acetophenone was obtained using KMnO4/CuSO4 the conversion of benzylic alcohols to the corresponding carbonyl
after 1hof sonochemical oxidation (eq 99), while the silent reac- compounds could be selectively performed in the presence of
aliphatic hydroxy groups (eq 104).
tion at room temperature gave, after the same time, just 8%. The
process can be performed as well in refluxing CH2Cl2, although
ultrasound irradiation significantly decreases the reaction time. A
OH KMnO4 O
KMnO4/zeolite reagent converts unsaturated secondary alcohols
(103)
to olefinic ketones under mild conditions (eq 100).85 In general, [bmim]BF4, rt, 1-2 h
R1 R2 R1 R2
83-97%
primary alcohols are oxidized more rapidly than secondary
R1 = Aryl, heteroaryl
alcohols (eq 101). However, oxidation of primary or secondary
R2 = H, Me
benzylic alcohols in the presence of aliphatic carbinols shows high
[bmim] = 1-Butyl-3-methylimidazolium
selectivity toward the benzylic alcohols. An example is depicted
in eq 102 using zirconyl chloride octahydrate (ZrOCl2·8H2O) as
a solid support.
OH
O
OH KMnO4
ME
KMnO4/CuSO4Å"5H2O
[bmim]BF4, rt, 1 h
Me
Me (99)
CH2Cl2 85%
HO
rt, ))), 1 h 100%
O
rt, 1 h 8%
reflux, 70 h 95%
ME
(104)
HO
OH
O
KMnO4/zeolite
Primary alcohols can also be converted into the corresponding
C5H11 1,2-dichloroethane
C5H11 (100)
carboxylic acids in good yield by means of potassium perman-
rt, 6 h, 87%
ganate. Examples using an IER as a solid support are shown in
eqs 105 and 106.66 The double bond moiety of Ä…,²-unsaturated
alcohols are preserved during the oxidation. Ketones are obtained
OH
in comparable yields from the oxidation of secondary aliphatic or
KMnO4/Al2O3
Me OH
aromatic alcohols (eqs 107 and 108.)66
+
solvent-free
KMnO4/IER
OH
O
OH
CH2Cl2, reflux, 4 h
94%
MeO
OH
Me
(101)
+
O
OH
100%
(105)
MeO
O
OH
O
KMnO4/ZrOCl2Å"8H2O
OH
OH
KMnO4/IER
(102)
Et2O, rt, 4 h, 90%
Ph
OH Ph (106)
OH
Ch2Cl2, reflux, 4.15 h
95%
Avoid Skin Contact with All Reagents
12 POTASSIUM PERMANGANATE
O
OH
eq 113. One exception was the p-nitrophenyl-substituted alcohol,
which generates a complex mixture in which no trace of the ketone
KMO4/IER
(107)
could be found.
CH2Cl2, reflux, 4.30 h
93% OH O
KMnO4/A-27
(113)
OH O
Ar CF3 4 Å, CH2Cl2, reflux, 2-7 h Ar CF3
KMnO4/IER
74-100%
(108)
CH2Cl2, reflux, 4 h
91% Oxidation of Ä…-hydroxyphosphonates to Ä…-ketophosphonates
is performed at room temperature with KMnO4 in dry benzene
A mixture of KMnO4 and MnO2 can be used as an effec-
or under solvent-free conditions supported onto neutral alumina,
tive oxidant for alcohols under both heterogeneous and solvent-
providing very good yields of the desired products (eq 114).107
free conditions.65 Both primary and secondary Ä…,²-unsaturated
O
alcohols were oxidized to the corresponding carbonyl compounds
KMnO4
R
P(OEt)2
without disruption of the double bond. Active MnO2 is able to
A: dry benzene, 3-12 h, 85-98%
oxidize alcohols to the corresponding ketones under solvent-free
OH
B: Al2O3, solvent-free, 4-15 h, 81-96%
conditions. However, the time required to complete the reaction
R = Ar, 3-py, Bn
is often a few days instead of hours as is observed when perman-
O
ganate is present (eqs 109 and 110).
R P(OEt)2 (114)
OH O
O
KMnO4/MnO2
(109)
rt
Allylic spiro-Å‚-lactones are obtained by the oxidative cycliza-
tion of Å‚-hydroxyl alkenes with potassium permanganate and
Conditions Yields (%) CuSO4·5H2O as the solid support in the presence of catalytic
amounts of water and tert-butyl alcohol (eq 115).108 It is be-
CH2Cl2, 4 h 83
lieved that in these oxidations the tert-butyl alcohol acts as a
solvent-free, 50 min 94
phase-transfer catalyst, and both water and tert-butyl alcohol form
a third phase (omega phase) over the inorganic solid. The reaction
))), solvent-free, 43 min 90
takes places on or at the interface.
O
OH
KMnO4/MnO2
H
(110)
KMnO4/CuSO4Å"5H2O
rt
(115)
OH
O
rt, H2O, tBuOH
O
CH2Cl2, 1 h, 62%
Conditions Yields (%)
CH2Cl2, 5 h 93
The oxidation of diols under heterogeneous conditions gave
solvent-free, 2 h
90 the corresponding ketones. 1,2-Bis(1-hydroxyethyl)benzene was
quantitatively oxidized to 1,2-diacetylbenzene after 1.5 h of sono-
))), solvent-free, 1 h 45 min 95
chemical reaction (eq 116).63 Reaction of hydroquinone with
potassium permanganate-silica sulfuric in the presence of wet sil-
Primary and secondary benzylic alcohols are converted into the
ica under solvent-free conditions gave p-benzoquinone in very
corresponding carbonyl compounds in relatively high yields in
good yield (eq 117).109
MeCN at room temperature (eqs 111 and 112).68
OH O
O
KMnO4
Ar OH
KMnO4/CuSO4Å"5H2O
(111)
Ar H
MeCN, rt, 0.30-3.30 h
(116)
))), CH2Cl2, 1.5 h, 100%
70-98%
OH O
R O
KMnO4
OH O
(112)
Ar OH Ar H
MeCN, rt, 0.30-3.30 h
40-98%
KMnO4/SiO2-OSO3H, wet SiO2
(117)
solvent-free, rt, 30 min, 95%
A polymer-supported reagent, potassium permanganate/
Amberlyst A-27, has been used to convert trifluoromethyl
OH O
aryl carbinols to trifluoromethyl ketones.106 The oxidation is
performed in refluxing CH2Cl2 (THF or toluene can also be used
if higher reaction temperatures are required) in the presence of Oxidation of Ethers, Acetals, and Thioacetals. Trimethyl-
4 Å molecular sieves as a dehydrating agent. The trifluoromethyl silyl- and tetrahydropyranyl ethers are efficiently deprotected to
aryl ketones are obtained in high yields and excellent purities the corresponding carbonyl compounds by KMnO4 supported
A list of General Abbreviations appears on the front Endpapers
POTASSIUM PERMANGANATE 13
on alumina, under solvent-free conditions, in very good yields 125).111 Oxidation of cinnamyl derivatives proceeded with the
(eqs 118 and 119).110 The rates and yields of the reactions in cleavage of the carbon-carbon double bond to give benzaldehyde.
the absence of Al2O3 are lower. Overoxidation of the regenerated aldehydes was not observed.
TMS
O O
KMnO4/Al2O3 n
KMnO4/silica Cl
O
(118)
Ar Ar (124)
R rt, 3-20 min R S S
MeCN, rt, 5-35 min
75-99%
R = H, Me
R1 R2
R1 R2
75-98%
n = 1, 2
THP
KMnO4/Al2O3
O
O R1 = Aryl, alkyl
rt, 5-20 min
(119)
R2 = H, aryl, alkyl
Ar R Ar R
75-95%
Oxidation of benzyl methyl ether with permanganate combined
X
O O
KMnO4/silica Cl
with iron(III) chloride in acetone solution gave the corresponding
(125)
esters in 86% yield, together with a 10% yield of benzaldehyde
MeCN, rt, 5-150 min
Ar R Ar R
(eq 120).79 70-92%
KMnO4/FeCl3
O
Ph
X = TMS, TBDMS, THP
Me
acetone, -78 °C to rt, 15 h
R = H, Me, Et, Ph
O
O
+
(120)
Alumina-supported permanganate also promotes the dethioac-
Ph H
Ph OMe
etalization of acyclic and cyclic thioacetals, under solvent-free
86% 10% conditions, to the corresponding carbonyl compounds in good
yields (eqs 126 and 127).112 The method proved to be particularly
Cyclic ethers are also converted into lactones under alumina-
effective with C-3 and C-20 dithiolane and dithiane derivatives
supported potassium permanganate in the presence of copper sul-
of steroidal ketones such as 5-cholesten-3-one and pregnenolone
fate pentahydrate (eq 121).64 When the Ä…-carbons are tertiary,
(eqs 128 and 129), which are usually removed under vigorous
the product is a dione, formed presumably by dehydration of the
conditions.
corresponding intramolecular bis(hemiacetal) (eq 122).
n
KMnO4/Al2O3
KMnO4/Al2O3/CuSO4Å"5H2O
O
(126)
(121) S S
solvent-free, rt, 5-25 min
rt, 6 h, 65%
O
O R1 R2
O R1 R2 85-99%
n = 1,2
KMnO4/Al2O3/CuSO4Å"5H2O
R1 = Aryl, alkyl
O
rt, 8 h, 60%
R2 = H, aryl, alkyl
(122) O
MeS
SMe
O
HO O
OH O
KMO4/Al2O3
(127)
solvent-free, rt, 20 min
Ethylene acetals are oxidized as well to the carbonyl com-
88%
t t
pounds using solvent-free alumina-supported potassium perman- Bu Bu
ganate (eq 123). Overoxidation of the products was not observed.
Cinnamaldehyde acetal was not converted to its correspond-
ing Ä…,²-unsaturated aldehyde, giving rise instead to many by-
products.110
3
KMnO4/Al2O3
KMnO4/Al2O3
O
solvent-free, rt, 25 min
O O (123)
rt, 5-15 min
91%
R1 R2
75-98% R1 R2
S
R1 = Aryl, alkyl S
R2 = H, aryl, alkyl
3
Potassium permanganate and silica chloride provides an
(128)
effective oxidizing system for selective oxidations of aromatic
or aliphatic cyclic thioacetals (1,3-dithiolanes and 1,3-dithiones),
and conversion of silyl- or tetrahydropyranyl ethers into their car-
O
bonyl compounds in dry MeCN at room temperature (eqs 124 and
Avoid Skin Contact with All Reagents
14 POTASSIUM PERMANGANATE
O OH
19
OMe
S
N
S
MeO
OAs
KMnO4/Al2O3
KMnO4/acetone
solvent-free, rt, 25 min
93% OAc
10% H2SO4
AcO
30%
OHC
OMe
AcO
O
MeO
As = OC OCH3
(129)
O
OH
H OMe
NH
AcO
MeO
OAs
The N,O-acetal, present in the 3-phenylhexahydro-5H-[1,3]- (132)
OAc
oxazolo[3,2-a]pyridine-5-carbonitrile, can be regarded as the
AcO
precursor of a lactam function after oxidation with KMnO4
HO2C
OMe
(eq 130).113 Neither degradation nor racemization at the CN group
MeO
was observed, leading to the 2-substituted-piperidin-6-one in an
80% yield. Presumably, the permanganate ion oxidized the Ä…- The utilization of potassium permanganate in aqueous sodium
amino ether function to produce an iminium intermediate. The
hydroxide allows the oxidation of phenylboronic aldehydes to the
reduction of the permanganate ion to manganese dioxide, in aque- corresponding acids, without affecting the boronic acid group, in
ous medium, liberated hydroxy ions, which could trap the iminium
preparative yield (eq 133).116
species. Subsequent opening of the oxazoline afforded the lactam
O
KMnO4
function.
(HO)2B
NaOH aq.
H
overnight
OH
Ph
Ph
90%
O
KMnO4
O
NC N
NC N O
(130) (133)
(HO)2B
acetone/H2O, rt
OH
80%
Oxidation of Organic Sulfur Compounds. Aliphatic and
aromatic thiols are converted into the corresponding disulfides
Oxidation of Aldehydes. Potassium permanganate has been
in good yields under very mild conditions, using solvent-free
successfully used in the synthesis of 4-amino-3-carboxy-²-carbo-
solid-supported potassium permanganate. No overoxidations to
line derivatives. In one of the final steps, treatment of the
sulfonic acids were observed in any case. Sulfides can be
corresponding aldehyde with potassium permanganate in acetone-
water afforded the 4-carboxylic acid in 84% yield (eq 131).114 converted to the sulfoxides or to the sulfones. Alumina-supported
permanganate affords the corresponding disulfides upon treat-
ment with thiols in good to excellent yields (eq 134).117 The
O
O
optimum molar ratio between the thiol and the oxidant is found
N
H
to be 1:1, but in the case of heterocyclic thiols an increase of the
CO2Et
KMnO4
thiol to permanganate ratio is required to complete the reaction.
N
Sulfoxides are selectively obtained by oxidation of the sulfides
acetone/H2O
3 h, 84%
with KMnO4-Al2O3 (eq 135).
N
CO2Et
KMnO4/Al2O3
R SH (134)
R S S R
O
O
rt, 15-30 min
+
N
K-O 75-90%
CO2Et
R = Aryl, heterocyclic, alkyl
N
(131)
O
KMnO4/Al2O3
N
R S R S
(135)
rt, 10-30 min R R
CO2Et
R = Aryl, alkyl
75-90%
A similar reaction has been used in the conversion of norditer- The reaction of thiols with potassium permanganate adsorbed
penoid alkaloids into aconane-type diterpenes. In this case, in on Montmorillonite K-10100 gave the corresponding disulphides
addition to the aldehyde being oxidized to a carboxylic acid, in good yields (eq 136). Alkyl- and aryl sulfides are oxidized to the
the pendant oxaziridine group was transformed to a formamide corresponding sulfones in a few hours at rt with no concomitant
(eq 132).115 formation of sulfoxides (eq 137).
A list of General Abbreviations appears on the front Endpapers
POTASSIUM PERMANGANATE 15
KMnO4/K-10
O
R SH R S S R (136)
rt, 25-70 min KMnO4, FeCl3
S
S S
74-96%
S acetone
S
R = Aryl, alkyl
O
O O
KMnO4/K-10
O O
(137)
R S R
S
rt, 2-6 h
S
R R S
S
(144)
S
75-85% S
R = Aryl, alkyl
O
O
Similar results are obtained with potassium permanganate
Heterogeneous oxidations of aromatic and aliphatic sulfides in
mixed with MnO2,65,118 or hydrated salts of transition metals,
acetonitrile solution give rise to the corresponding sulfones in
such as copper sulfate pentahydrate (eqs 138 and 139),64 as pro-
good yields (eqs 145 and 146).68
moters of heterogeneous permanganate oxidation. Sulfones are
more rapidly obtained when the reaction is assisted by microwave
KMnO4, rt
irradiation.
O O (145)
CH3CN, 55 h, 95%
S
S
CH2Cl2, 72 h, 25%
KMnO4/CuSO4Å"5H2O
R SH R S S R (138)
rt, 7-15 min
O
95-100%
R = Aryl, alkyl O
KMnO4, rt
S S
(146)
Alkyl Alkyl Alkyl Alkyl
CH3CN, 5-7 h, 85-93%
O O
KMnO4/CuSO4Å"5H2O
R S R (139)
S
rt, 5 15 min
R R
Reaction of thiazolines with KMnO4 under phase-transfer
R = Aryl, alkyl 85 90%
catalysis conditions gave the corresponding thiazoles (eq 147).
However, addition of 1 equiv of benzoic acid resulted in a com-
Oxidation of thiols and sulfides with KMnO4 in the presence
plete change in favor of S-oxidation, affording the thiazoline S,S-
of IER Rexyn 101H in refluxing CH2Cl2 gave disulfides and sul-
dioxides in 85 93% yield.119 The oxidation was carried out in an
fones, respectively, in excellent yields (eqs 140 and 141).66 Alkyl-
aqueous solution of KMnO4 (2 equiv) and benzyltriethylammo-
and aryl sulfides are converted into the corresponding sulfones.
nium chloride (0.1 equiv) at rt in CH2Cl2 (eq 148).
The observation that benzyl phenyl sulfide and dibenzyl sulfide
gave the related sulfones indicated that the reaction proceeds by
R
R
way of an oxygen transfer mechanism, instead of the electron N
N KMnO4, BnEt3NCl
(147)
transfer which would have formed substantial amounts of ben-
CH2Cl2, rt, 85-93%
Ph
Ph
S
S
zaldehyde.
R
KMnO4/IER
R
R
R
R SH R S S R (140)
N
CH2Cl2, reflux, 2-2.45 h
N KMnO4, BnEt3NCl, PhCO2H
(148)
R = Bn, alkyl
94-96%
Ph
CH2Cl2, rt, 85-93%
Ph S
S
O O
O O
KMnO4/IER
R S R (141)
S
CH2Cl2, reflux, 4-7 h
R
R This reagent system gave excellent results in converting the
85-95%
R = Aryl, alkyl exocyclic C=S of thiazolidine-2-thines into C = O (eq 149).
Moreover this procedure is suitable for a variety of simple
sulfides, dibenzylsulfoxide, thiazolidines, and thiaxolidin-2-ones
Treatment of benzyl phenyl sulfide with permanganate and
(eqs 150 153).
iron(III) chloride in either acetone or MeCN gave the correspond-
ing sulfone in excellent yield (eq 142).79,80 Since the ultimate
S KMnO4, BnEt3NCl, PhCO2H S
product is a sulfone, the initially formed sulfoxide must undergo
(149)
CH2Cl2, rt, 3 h, 70%
S O
a subsequent rapid oxidation. This conclusion is consistent with
S S
competitive experiments in which incompounds containing both
sulfide and sulfoxide functionalities, the latter is preferentially O O
KMnO4, BnEt3NCl, PhCO2H
(150)
R S R
S
oxidized (eqs 143 and 144).
CH2Cl2, rt, 3 h, 52-82%
R R
R = Aryl, alkyl
O O
KMnO4, FeCl3
S
O
(142)
S
KMnO4, BnEt3NCl, PhCO2H O O
acetone, 0 °C
(151)
S
S
98%
CH2Cl2, rt, 3 h, 75%
Bn Bn
Bn Bn
RR
R
Ac
Ac
R
N
N KMnO4, BnEt3NCl, PhCO2H
O
(152)
O O
KMnO4, FeCl3
R
CH2Cl2, rt, 3 h, 50-95%
R S
S S S S
(143) S
acetone O
O
Avoid Skin Contact with All Reagents
16 POTASSIUM PERMANGANATE
HO
Et
Et
Bn H
Bn
NH NO2
H
N
N KMnO4, BnEt3NCl, PhCO2H
(153)
O
KMnO4, H2O
CH2Cl2, rt, 3 h, 72%
O S
S
(159)
O
O N N
rt, 20 h
60-65%
SO3H SO3H
Amine Oxidation. The heterogeneous oxidation of primary
aliphatic- and aromatic amines using potassium permanganate ad-
Cleavage of Carbon Nitrogen Double Bonds. Potassium
sorbed onto hydrated copper sulfate gives rise to ketones and azo
permanganate supported on a solid support regenerates carbonyl
compounds, respectively, in nearly quantitative yields (eqs 154
compounds from oximes. No overoxidation of the correspond-
and 155).120 No oxidation of the benzylic positions are observed
ing carbonyl compounds to carboxylic acids was observed. The
in the case of alkylanilines. Other solid supports such as iron(II)
deoximation reaction with KMnO4-Al2O3 proceeded under
sulfate heptahydrate have been used (eqs 156 and 157).121
ć%
solvent-free conditions at 50 C in good to excellent yields
(eq 160).123 In addition, Ä…,²-unsaturated oximes were selec-
KMnO4/CuSO4Å"5H2O
tively oxidized to the corresponding enone. The carbon-carbon
NH2 CH2Cl2, rt or reflux, 1-2 d O (154)
double bond remained unaltered (eq 161). Under these reac-
87-100%
tion conditions, ketoximines can be exclusively cleaved in the
presence of aldoximes. Organic solvents, such as acetone or ether,
KMnO4/CuSO4Å"5H2O
(155) can also be used to perform the oxidative cleavage of ketoximines
Ar NH2 CH2Cl2, rt or reflux, 1-2 d Ar N N Ar
to ketones.124
78-100%
Ar NH2 = Aniline, 2- and 4-butylaniline, 2- and 4- isopropylaniline,
OH
2- and 4- sec -butylaniline, 4-iodoaniline, 4-chloroaniline O
N
KMnO4/Al2O3
R1 R2 (160)
R1 R2 50 °C, 15-40 min
NH2
78-99%
KMnO4, FeSO4Å"7H2O
R1 = Aryl, naphthyl, alkyl
(156)
N N
CH2Cl2, reflux, 5 h
R2 = H, Me, Ph
95%
OH
N
O
O
KMnO4, FeSO4Å"7H2O KMnO4/Al2O3
(157) (161)
Ph R 50 °C, 10 40 min
Ph R
NH2 CH2Cl2, reflux, 5 h
H
87 92%
80%
R = H, Me, Ph
Primary aromatic amines are also oxidatively coupled under
Oxidation using KMnO4 in the presence of montmorillonite
mild conditions using alumina and copper sulfate pentahydrate as
K-10 occurs under solvent-free conditions in good yields
a solid support (eq 158).64 The presence of an electron-withdra-
(eq 162).125 Semicarbazones, phenylhydrazones, and azines were
wing substituent such as a chloro group decreased the reaction
also transformed to their corresponding carbonyl compounds in
rate but not the yield.
80 96% yields (eqs 163 165). However, 2,4-dinitrophenylhydra-
zones are resistant to this reagent system and remained intact in
KMnO4/Al2O3/CuSO4Å"5H2O
Ar N N Ar (158)
2 Ar NH2 the reaction mixture.
rt, 5-20 h
70-85%
OH
N
O
Me
KMnO4/K-10
R1 R2
R1 R2 (162)
rt, 5 60 min
Ar = Ph,
Me, Cl
R1 = Aryl or alkyl 85 97%
R2 = H, Me, Ph
Me
NHCONH2
O
Oxidation of 5-hydroxyaminopyridine-2-sulfonic acid to 5- N
KMnO4/K-10
(163)
nitropyridine-2-sulfonic acid may be performed selectively by
rt, 15 20 min
Ar H
Ar H
sodium perborate in acetic acid, bleach in water, or potassium
80 96%
1
permanganate in water, with the latter being preferred. By H
NMR this process appeared to provide quantitative conversion to
NHPh
N O
product, but high isolated yields were difficult to achieve, proba- KMnO4/K-10
(164)
bly due to inorganic impurities present even after treatment with
rt, 10 20 min
Ar R1 R1 R2
acidic ion exchange resin. Isolated yields were in the range of 82 96%
R1= H, Me
60 65% (eq 159).122
A list of General Abbreviations appears on the front Endpapers
POTASSIUM PERMANGANATE 17
Ar
KMnO4 (2 equiv)
COOH
O
CH2Cl2, rt, 20 h
N O
KMnO4/K-10
80%
N
(165)
rt, 25 30 min
R1 R2 O
83 95%
Ar R1
H
R1= H, Me (169)
O
Other solid supports such as wet silica promote the KMnO4
COOH
O
oxidative cleavage of semicarbazones and phenylhydrazones KMnO4 (2 equiv)
(170)
under solvent-free conditions at rt (eq 166).126 This procedure
COOH CH2Cl2, rt, 20 h H
is fairly effective also for sterically hindered semicarbazones 75%
(eq 167). Molecules bearing acid-sensitive as well as base-sensi-
tive functional groups as tert-butoxycarbonyl, tetrahydropyranyl
O
HO COOH
ether, and aliphatic or aromatic hydroxyl or sulfide groups re-
KMnO4 (1.5 equiv)
(171)
main intact under the reaction conditions. Cinnamaldehyde semi-
CH2Cl2, rt, 20 h
carbazone underwent oxidative cleavage without affecting the
90%
double bond moiety.
2,5-Disubstituted 1,3,4-oxadiazoles were prepared by oxidation
of 1-aroyl-2-arylidene hydrazines with KMnO4 on the surface of
X
N O
KMnO4/wet SiO2 silica gel or montmorillonite K-10, or with mixtures of acetone
(166)
and water under microwave (MW) irradiation (eq 172).129
rt, 15 45 min
R1 R2 R1 R2
72 98%
O
X = NHCONH2, NHPh
KMnO4
N R2
R1 = Aryl, alkyl
SiO2, MW, 8-25 min, 61-96%
R1 N
H
R2 = H, Me acetone/water, MW, 8-22 min, 64-96%
R1 = Ph, Me, 4-ClC6H4
R2 = Ar, Me, CH=CHCH3
N N
(172)
KMnO4/wet SiO2
R2
R1 O
(167)
NHCONH2 rt, 30 min
O
N
80%
Various types of 2-imidazolines can be efficiently oxidized
to the corresponding imidazoles using potassium permanganate
supported on silica gel under mild conditions at room temper-
ature. Chemoselective oxidation in the present of other oxidiz-
Miscellaneous Oxidations. Oxidation of secondary Ä…-hydro-
able functional groups was also accomplished by this reagent sys-
xysilanes to acylsilanes is performed by a mild procedure using
tem (eq 173).130 Selective oxidation of 2-alkylimidazolines in the
permanganate supported on neutral alumina. Due to the lability of
presence of 2-arylimidazolines was achieved using alumina-
the acylsilane to oxidizing reagents, a biphasic mixture of hexane-
supported potassium permanganate.131
water was used as solvent to limit contact between the inorganic
reagent and the product (eq 168).127
N N
KMnO4/SiO2
(173)
CH3CN, rt, 2 h
N N
OH
85%
H H
Cl Cl
KMnO4/Al2O3-H2O
SiMe3
hexane, 1 4 h
Oxidation of Ä…-amido nitro derivatives with permanganate
80%
MeO
potassium in phosphate buffer (pH = 11) lead, after acidic work up,
to the corresponding N-protected Ä…-amino acids in good yield.132
O
When a secondary nitro group is present in the framework it is
SiMe2R2 (168) also oxidized to the parent carbonyl derivative affording the keto
amino acid or aminodicarboxylic acid (eqs 174 176). Alkenes are
MeO
incompatible with this reaction conditions.
NO2
1. KMnO4/phosphate buffer
O
A simple and efficient decarboxylation of aromatic carboxylic
acids can be performed by KMnO4 in nonaqueous media. No vig-
2. H3O+
Ph
N Ph
orous conditions or catalysts were required. The reaction is carried
H
O COOH
out in CH2Cl2 or CHCl3 at room temperature. No overoxidation
(174)
of the aldehydes was observed. Some examples are depicted in
Ph
N
Ph
H
(eqs 169 171).128
Avoid Skin Contact with All Reagents
18 POTASSIUM PERMANGANATE
KMnO4/BnNEt3Cl/TMSCl
NO2
S
1. KMnO4/phosphate buffer
O
Ph
5 CH2Cl2, -78 to 25 °C
C4H9 2. H3O+
80%
Ph
N
O
H
(181)
NO2
S
Ph
5
O COOH
KMnO4 in liquid ammonia can be used as an efficient oxidant
C4H9 (175)
Ph
N
for the oxidation of ÃH-adducts formed in the addition of car-
H
O banions to nitroarenes (eq 182).134-136 In these oxidative nucle-
ophilic aromatic substitution of hydrogen reactions (ONASH), the
NO2
permanganate anion presumably attacks the adduct at the addition
1. KMnO4/phosphate buffer
O
site of the nucleophile.
2. H3O+
Ph
N NO2
4
-
H
NO2
O COOH
NO2 Me
COOH (176)
-
Ph
KMnO4/NH3(liq)
N 4 Ph CN
H
87%
H CN
Ph
Trimethylsilyl chloride and benzyltriethylammonium perman-
Me
ganate, easily prepared with KMnO4 and the phase-transfer
reagent benzyltriethylammonium chloride, chemo- and stereo-
NO2
selectively dichlorinate alkenes, cleave epoxides, and oxidize
sulfides to sulfoxides in high yields (eqs 177 181).133 The
(182)
emerald-green manganese complex, KMnO4/BnNEt3Cl/TMSCl,
ć%
reacts with alkenes at 0 CinCH2Cl2 exclusively by anti-dichlori-
CN
nation, with the exception of the aromatic olefins which gave a
Ph
Me
mixture of syn- and anti-dichlorides. Reaction with epoxides takes
place with an excess of TMSCl. In benzylic oxiranes, ring opening
Similarly, the direct coupling of amines, amides, and ketones
to form benzylic chlorides is preferred, while in alkyl epoxides,
with nitroarenes and nitronaphthalenes is reported through ox-
chloride insertion is performed at the less sterically hindered
idative activated nucleophilic aromatic substitution promoted by
position (eqs 179 and 180). Sulfoxides are obtained by inverse
fluoride anions as the nucleophilic activating agent and KMnO4
addition of the manganese reagent (1 2 equiv) to the sulfide.
as the oxidant (eq 183).137
Alkenyl sulfides display excellent chemoselectivity, with only
NO2 NO2
traces of dichlorinated olefin (eq 181).
NuH, TBAF·3H2O
(183)
Cl
KMnO4, DMF
KMnO4/BnNEt3Cl/TMSCl
Ph
(177)
Ph
NO2 NO2
42-75%
Ph
CH2Cl2, 0 °C to rt Ph
Nu
95%
Cl
Nu = iPrNH2, PhNH2, PhCONH2, MeCOEt
Cl
KMnO4/BnNEt3Cl/TMSCl
Related Reagents. Potassium Permanganate Copper(II) Sul-
(178)
O
O
CH2Cl2, 0 °C to rt fate; Sodium Periodate Potassium Permanganate.
Cl
60%
O KMnO4/BnNEt3Cl/TMSCl
1. Stewart, R. In Oxidation in Organic Chemistry; Wiberg, K. B., Ed.;
Ph
CH2Cl2, 20 °C, 50 min
Academic: New York, 1965; Part A, Chapter 1.
89%
2. Lee, D. G. In Oxidation in Organic Chemistry; Trahanovsky, W. S.,
Cl Cl
Ed.; Academic: New York, 1962; Part D, Chapter 2.
(179)
+
3. Arndt, D. Manganese Compounds as Oxidizing Agents in Organic
Ph Ph
Chemistry; Open Court: La Salle, IL, 1981; Chapter 5. Lee, D. G.
OH OH
The Oxidation of Organic Compounds by Permanganate Ion and
(1:4)
Hexavalent Chromium; Open Court: La Salle, IL, 1980.
4. Fatiadi, A. J., Synthesis 1987, 85.
O
KMnO4/BnNEt3Cl/TMSCl
5. Coleman, J. E.; Ricciuti, C.; Swern, D., J. Am. Chem. Soc. 1956, 78,
C5H11
CH2Cl2, 20 °C, 50 min
5342.
85%
6. Frigerio, N. A., J. Am. Chem. Soc. 1969, 91, 6200. Perez-Benito, J.;
Arias, C.; Brillas, E., Gazz. Chim. Ital. 1992, 122, 181.
OH Cl
(180)
+ 7. Lee, D. G.; Chen, T., J. Org. Chem. 1991, 56, 5346.
Cl OH
C5H11 C5H11
8. Sam, D. J.; Simmons, H. E., J. Am. Chem. Soc. 1972, 94, 4024.
(6:1)
9. Noureldin, N. A.; Lee, D. G., Tetrahedron Lett. 1981, 22, 4889.
A list of General Abbreviations appears on the front Endpapers
POTASSIUM PERMANGANATE 19
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11. Bromby, N. G.; Peters, A. T.; Rowe, F. M., J. Chem. Soc. 1943, 144.
50. Farrar, W. V., J. Chem. Soc. 1954, 3253.
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A list of General Abbreviations appears on the front Endpapers