HYDROGEN PEROXIDE UREA 1
perhydrolyzed. A comparison of the diastereoselective epoxida-
Hydrogen Peroxide Urea1
tions of a steroidal allylic alcohol has been carried out using a
range of peroxy acids, including peracetic acid generated by the
O
interaction of acetic anhydride with UHP.7
H
H2N N
H
UHP, Na2HPO4, Ac2O
H
(1)
O
O H
CH2Cl2, rt, 15 h
H O
79%
UHP, Na2HPO4
[124-43-6] CH6N2O3 (MW 94.09)
(CF3CO)2O
(2)
InChI = 1/CH4N2O.H2O2/c2-1(3)4;1-2/h(H4,2,3,4);1-2H/f/h2- O
CH2Cl2, ", 0.5 h
3H2;
88%
InChIKey = AQLJVWUFPCUVLO-IMJSYYCQCZ
The epoxidation of electron-deficient alkenes like methyl
(alternative to 90% hydrogen peroxide as a source of anhydrous
methacrylate can also be achieved using the trifluoroacetic
hydrogen peroxide for use in oxidation reactions)
anhydride method. In the case of ą,�-unsaturated ketones such
Alternate Name: UHP. as isophorone (eq 3) and nitro alkenes such as �-methyl-�-
ć%
Physical Data: mp 84 86 C (dec).2 nitrostyrene (eq 4), alkaline hydrogen peroxide has been
Solubility: sol water and alcohols; low solubility in organic generated from UHP.
solvents such as dichloromethane.
OO
Form Supplied in: white crystalline powder with urea as impurity;
O
UHP, NaOH
commercially available.
(3)
Drying: over calcium chloride in a desiccator.
MeOH
Preparative Method: made by the recrystallization of Urea from 68%
aqueous Hydrogen Peroxide.
O
NO2 UHP, NaOH NO2
Handling, Storage, and Precautions: the pure material should be
(4)
stored at low temperature but the commericial material, which
MeOH, 0 5 �C
94%
has a purity of ca. 90%, may be stored at rt. In a sufficiently
forcing test, it can be made to explode; its decomposition is
The selective epoxidation of compounds such as ą-ionone can
ć%
acceleratory above 82 C. Conduct work with this reagent in an
also be achieved. The result of an epoxidation reaction frequently
efficient fume hood behind a polycarbonate safety screen.
depends on the reagent and precise reaction conditions. This is
exemplified in the reactions shown in eq 5. When using per-
oxytrifluoroacetic acid generated conventionally, water that is
always present diverts the reaction exclusively to the hemiacetal
Original Commentary
(1). However, when using the UHP method, the spiroacetal (2)
predominates over the other product.8
Harry Heaney
O HO
Loughborough University of Technology, Loughborough, UK
O
OH
O
Epoxidation Reactions. The hydrogen peroxide urea com-
plex, which is normally known as urea hydrogen peroxide (UHP), NC
CF3CO3H
OH
has been used in anhydrous organic solvents in combination with
O (1)
O
a number of carboxylic anhydrides together with disodium hy-
O
drogen phosphate for the epoxidation of a wide range of alkenes.
(5)
CN
The carboxylic anhydride of choice depends on the electron den-
(CF3CO)2O
UHP
sity in the double bond.3 With electron-rich alkenes such as ą-
OH
O
methylstyrene and ą-pinene (eq 1), good yields of the expected
", 19 h
O
products can be obtained by using Acetic Anhydride. Other an-
O
O + (1)
hydrides have also been used; for example, the epoxide from
trans-stilbene is obtained in 80% yield using Maleic Anhydride.4
NC
Monoperoxymaleic acid, prepared by the reaction of maleic anhy-
OH
dride with 90% aqueous hydrogen peroxide, is more reactive than (2)
7:2
other common peroxy acids with the exception of Trifluoroper-
Baeyer Villiger and Related Reactions. The oxidation of
acetic Acid.5 With relatively nonnucleophilic and nonvolatile ter-
aldehydes and ketones to afford esters and lactones can be
minal alkenes such as 1-octene, a good yield of the epoxide can be
achieved using a variety of peroxycarboxylic acids. The ease with
obtained by substituting Trifluoroacetic Anhydride for the acetic
which the reaction occurs is related to the strength of the conjugate
anhydride (eq 2). The addition of Imidazole increases the rate at
acid of the leaving group and so the stronger the carboxylic acid
which epoxidation reactions proceed when using UHP and acetic
the more powerful is the peroxy acid in its oxidation reactions.
anhydride.6 Presumably N-acetylimidazole is formed and rapidly
Avoid Skin Contact with All Reagents
2 HYDROGEN PEROXIDE UREA
Reactions involving ketones are frequently slow when using First Update
weakly acidic peroxy acids and so the majority of the reactions
Francesca Cardona & Andrea Goti
using UHP have been carried out with trifluoroacetic anhydride
Universitą di Firenze, Firenze, Italy
as the coreactant (eqs 6 8).
The hydrogen peroxide urea complex (UHP) has been used as
UHP, Na2HPO4
reagent for different oxidation reactions such as epoxidations,1 8
(CF3CO)2O
O (6) Baeyer Villiger and related reactions, and some heteroatom
CH2Cl2, rt, 17 h
O
O oxidations,9 11 in combination with stoichiometric amounts of
98%
various reagents, in anhydrous organic solvents.
UHP represents a valid and safer anhydrous alternative to aq
H2O2, also allowing the use of nonaqueous solvents.
O As per the previous e-EROS report, a great effort has been
O
UHP, Na2HPO4
O
devoted to develop more environmentally benign oxidations,
(CF3CO)2O
(7) which employ stoichiometric UHP in combination with metal cat-
CH2Cl2, ", 2 h
alysts, or reagents and catalysts immobilized on a solid support
76%
(heterogeneous reagents and catalysts), or even metal-free and
solvent-free systems.
O
UHP, Na2HPO4
(CF3CO)2O
O
Epoxidation Reactions. A modification of the reported use
(8)
of UHP in combination with carboxylic anhydrides for the epoxi-
CH2Cl2, rt, 4 h
O
94%
dation of alkenes1 7 has been studied by heterogenization of
the anhydride. A new polystyrene-divinylbenzene (PS-DVB) sup-
Dakin reactions, where an aromatic aldehyde has an electron
ported phthalic anhydride was recently introduced and employed,
releasing substituent either ortho or para to the formyl group, can
together with UHP, for the epoxidation of a variety of substituted
be carried out using UHP acetic anhydride as shown in eq 9.
and terminal olefins (eq 13).12
In the absence of suitable activating substituents, hydrogen
migration occurs in place of aryl migration and the product is
O
O
then a carboxylic acid (eq 10). This is a potentially valuable way O
O O
n
O
of converting a formyl group into a carboxyl group.
O
CHO OH
UHP, Na2HPO4
UHP, CH2Cl2
(CF3CO)2O
OMe OMe
(9)
O
CH2Cl2, rt, 19 h
81%
(13)
75%
CHO CO2H
UHP, Na2HPO4
(CF3CO)2O
(10)
The dicyclohexylcarbodiimide (DCC)-UHP system, in MeOH
CH2Cl2, rt, 19 h
95%
OMe OMe
is able to transfer an oxygen atom to terminal and substituted
double bonds.13 The reaction probably occurs via an adduct
between DCC and H2O2, in which an intramolecular H-bond
Heteroatom Oxidation. The first example of the use of
renders hydrogen peroxide more electrophylic (eq 14).
UHP in organic chemistry involved the formation of the N-oxide
shown in eq 11,9 and, in a modification of the UHP method, ph-
thalic anhydride has been used to oxidize 4-t-butylpyridine to the
N-oxide in 93% yield.10 The oxidation of aliphatic aldoximes
N
using UHP trifluoroacetic anhydride has been achieved in good
HN
O
C H2O2
+
yields with retention of configuration at neighboring chiral centers C
+
O
N
(eq 12).11
N
H
CF3 CF3
CF3CO2H, H2SO4
(11)
UHP
F3C N N O F3C +N N O
60%
H
O H
O (14)
HN +
HN
O
C
O
OBn OBn O
N HN
H
UHP, (MeCO)2O
O O
(12)
O O
NOH NO2
A list of General Abbreviations appears on the front Endpapers
HYDROGEN PEROXIDE UREA 3
OSiMe3 1. MTO, UHP, Py O
Several cyclic vinylsilanes were epoxidized with the DCC/UHP
OH
CH3CN/CH3COOH
system.14 Epoxidation of electron-deficient olefins requires the
MeO Ph
(18)
MeO
2. F 
Ph
presence of a base.3 The reaction time needed to oxidize sev-
Ph Ph
eral ą,�-unsaturated ketones with aqueous sodium hydroxide and
75%
UHP was substantially reduced by means of microwave irradi-
ation, even for sterically hindered substrates.15 Quinones were
Epoxidation of glycals affords extremely labile epoxides, but
oxidized efficiently using UHP and K2CO3, in alcohol or
interesting sugar derivatives can be obtained in the presence
dichloromethane.16 Excellent yields and enantioselectivities were
of suitable nucleophiles. The MTO-catalyzed epoxidation
achieved in the nonaqueous Juli� oxidation of enones employing
methanolysis of glycals afforded the methyl glycosides in high
polymeric ą-amino acids (eq 15).17
yields and good diastereoselectivities (eq 19).23 The reaction was
DBU also performed using heterogeneous catalysts containing MTO
poly-(L)-leucine O
O
complexed to nitrogen-containing ligands or microencapsulated
Ph H
UHP
(15)
in polystyrene.23b
THF
Ph Ph H Ph
O
OBn
MTO (2 mol %), UHP (3 equiv)
MeOH, rt, then Py, Ac2O
O
100% yield
BnO
BnO
>95% ee
87%
OBn
Regarding metal-catalyzed epoxidations, the use of rhenium- OBn
AcO
O
O
based systems for the epoxidation of alkenes with UHP as sto- BnO
(19)
BnO
+
BnO
ichiometric oxidant has expanded considerably in scope and BnO
OMe
OAc
applicability during the past years.
OMe
5.3:1
In the original report on alkene epoxidation using methyltriox-
orhenium (MTO) as catalyst, Herrmann and co-workers employed
In the presence of dibutylphosphate as nucleophile glycosyl-
a dry solution of hydrogen peroxide in tert-butanol as the termi-
phosphates, good glycosyl donors were formed.23a In this case a
nal oxidant, prepared by mixing tert-butanol and aqueous hydro-
gen peroxide followed by the addition of anhydrous MgSO4.18 room temperature ionic liquid was used as solvent, in the presence
of a 5-fold excess of dibutylphosphate. Later, it was demonstrated
Epoxidation of various alkenes using 0.1 1 mol % of MTO and
that introduction of a substoichiometric amount of nitrogen lig-
the H2O2/t-BuOH solution generally resulted in high conversion
ands, such as pyridine or imidazole, resulted in acceleration of the
to the corresponding epoxides, but a significant amount of trans-
reaction and improvement of epoxidation selectivities (eq 20).
1,2-diols was often formed via ring opening of the epoxide. The
Moreover, the reacting dibutylphosphate could be reduced to
use of UHP instead of hydrogen peroxide resulted in substantially
stoichiometric amounts.24
better selectivity for several olefins avoiding ring cleavage of the
epoxides (eq 16 vs. eq 17).19 Indeed, the urea produced during
1. MTO (4 mol %), UHP (3 equiv)
DBP (1.2 equiv), imidazole (0.5 equiv)
OBn
the consumption of UHP lowers the acidity of the medium, thus
THF
O
BnO
preventing acid-catalyzed ring opening.
BnO
2. Py, Ac2O, 69% (2 steps)
O
OBn
OBn
MTO (1 mol %)
(16) AcO
O O O
BnO BnO
UHP (1 equiv) (20)
+
BnO BnO
OP(OBu)2
CH2Cl2
OAc
OP(OBu)2
HO OH
14:1
O
MTO (1 mol %)
(17)
H2O2 85% (1 equiv)
A highly selective exo-epoxidation of norbornene was carried
CH2Cl2
out over vanadium-substituted phosphomolybdic acid catalysts
as the major product
with UHP. Thanks to the controlled release of hydrogen peroxide,
the absence of water and the less acidic character of the reaction
In an attempt to eliminate chlorinated solvents to develop a
medium, a 97% of the epoxide was obtained (eq 21).25
cleaner environment for the MTO-catalyzed epoxidation reac-
tions, a room temperature ionic liquid, namely 1-ethyl-3-methyli-
UHP
midazolium tetrafluoroboratre, [emim]BF4, was used as solvent.20
H4[PVMo11O40], 0012 equiv
O
(21)
Excellent conversions in the oxidation of a wide variety of alkenes
CH3CN, 60 �C, 4 h
for the corresponding epoxides were obtained.
67%
Methyltrioxorhenium (MTO) in combination with UHP also
allowed the oxidation of uracil derivatives into the correspond- Limited examples of metal-catalyzed enantioselective epoxida-
ing 5,6-epoxides with better yields than using aqueous hydrogen tions have been reported. Complete conversions and good enan-
peroxide.21 tiomeric excesses (64 100%) were achieved in the asymmetric
The MTO-catalyzed oxidation of methyl trimethylsilyl ketene epoxidation of chromenes and indene using UHP as oxidant and a
acetals afforded ą-hydroxyesters in good yields after desilylation novel dimeric homochiral Mn(III) Schiff base as catalyst. The re-
(eq 18).22 actions were carried out in the presence of carboxylate salts and ni-
Avoid Skin Contact with All Reagents
4 HYDROGEN PEROXIDE UREA
HO
(CetylPy)10[H2W12O42]/FAp
trogen and oxygen coordinating cocatalysts. However, the epoxi-
dation of styrene proceeded with incomplete conversion and only UHP (2.5 equiv)
23% ee.26 Modification of the catalyst and use of pyridine N-oxide
(25)
as cocatalyst allowed improvement of the ee to 61% (eq 22).27
O
UHP in place of aqueous hydrogen peroxide allowed recycle and
OH
reuse of catalyst, albeit with decreasing efficiency in subsequent
99% conv
catalytic runs.
78% yield
O
catalyst (1 mol %), PyNO (8 mol %)
Due to the cost and/or toxicity of many of the reported metal
(22)
UHP (1.2 equiv)
catalysts, the development of a metal-free epoxidation process is
CH2Cl2/MeOH, 2 �C, 5 h
of great value. A metal-free epoxidation using UHP in combina-
50%
61% ee tion with hexafluoro-2-propanol (HFIP) was recently developed.32
Ph HFIP exhibited a unique ability to release and activate hydrogen
Ph Ph
Ph
peroxide from UHP. Activation of oxygen through a strong hy-
N N N N
drogen bond between H2O2 and the acidic hydrogen of HFIP was
Mn Mn
t-Bu O O
catalyst = O O t-Bu
suggested. Trifluoroethanol (TFE) was less efficient than HFIP.
Cl
Cl
With reactive olefins no catalyst was required (eq 26): a com-
t-Bu t-Bu
t-Bu t-Bu
plete conversion of cyclooctene was achieved after 10 h, while the
same reaction with 30% hydrogen peroxide was incomplete after
Several heterogeneous systems were developed by immobiliza-
24 h. With less reactive monosubstituted olefins, epoxides were
tion of the catalysts on solid supports, in order to simplify reac-
obtained in high yield by using catalytic amounts (3 5 mol %) of
tion procedures and to increase the stability of the catalyst. It
perfluorodecan-2-one.
was reported that MTO supported on niobia catalyzed the epoxi-
dation of simple olefins and several fatty oils using UHP as the
terminal oxidant.28 With this procedure, several fatty acids were
UHP (3 equiv)
O (26)
epoxidized in high yields (80 100%) in less than 2 h (eq 23).
HFIP
The reaction could also be performed without solvent. Moreover,
10 h, 100%
the catalyst could be recycled and reused without loss of activity.
A green chemoenzymatic procedure for oxidation of olefins
employs Novozym 435, the immobilized form of Candida antar-
O
MTO/Nb2O5
tica lipase B, UHP and ethyl acetate as solvent. Peracetic acid was
UHP
COOH
COOH
(23)
generated in situ through oxidation of ethyl acetate by UHP.33 A
50 �C, 10 min
7 7
7 7
100% minimal amount of enzyme was necessary to show the catalytic
effect. On recycling, the enzyme maintained its catalytic activity
up to six epoxidations. Several alkenes were oxidized with yields
Microporous molecular sieves such as titanium silicates
ranging from 75 to 100% (eq 27).
(TS-1 and TS-2) were employed in highly selective of olefin epoxi-
dations with UHP.29
TS-1 in combination with UHP allowed chemo- and diastero-
Novozyme 435
selective epoxidation of chiral allylic alcohols (eq 24), while the O
(27)
UHP (1.1 equiv)
use of dilute aqueous hydrogen peroxide solution caused migra-
AcOEt, 2 h
100%
tion and/or substitution of the hydroxy group.30
OH OH OH
Heteroatom Oxidation. Nitrogen heterocycles are oxidized
TS-1, UHP
+ (24)
O O
to N-oxides with UHP in the presence of strong acids.9 An effi-
acetone
cient solvent-free oxidation using a 2 molar excess of UHP in the
erythro
threo
absence of solvent was recently developed (eq 28).34
95:5
N
N
Several terminal, cyclic, and substituted olefins were epox-
UHP (2 equiv)
(28)
idized using cetylpyridinium dodecatungstate on fluoroapatite
85 �C, 45 min
N
N
(FAp), a new reusable solid and efficient catalyst for solvent free- +
92%
_
O
epoxidations.31 The solid phase could be recovered and reused up
(5% of the dioxide)
to five times without loss of efficiency. Oxidations of alkenyl alco-
hols having a three or four carbon atom chain between the double
bond and the hydroxy group also proceeded at room temperature Using 1 equiv of UHP and 1 equiv of maleic anhydride, several
affording the cyclic compounds via epoxide formation (eq 25). N-alkyl imines were oxidized to the corresponding oxaziridines,35
Under similar conditions, secondary alcohols were slowly oxi- while methyltrioxorhenium (MTO) catalyzed oxidation afforded
dized to ketones. the corresponding nitrones (eq 29).36
A list of General Abbreviations appears on the front Endpapers
HYDROGEN PEROXIDE UREA 5
UHP (1 equiv) O
The triphenylphosphine ligands in the catalyst stopped the reac-
N
maleic anhydride tion at the sulfoxide stage more efficiently than MTO (eq 33).43
CH2Ph
Ph
(1 equiv)
On the contrary, in the presence of trifluoroacetic anhydride,
MeOH, 0 �C, 40 min
oxidation by UHP proceeds further to the sulfone.44
95%
(Ph3P)2ReOCl3
(33)
PhCH2SMe3 PhCH2SOMe
PhCH NCH2Ph
UHP, MeCN
(29)
rt, 18 h, 90%
High levels of enantioselectivity were reached in the sulfoxida-
MTO (2 mol %)
UHP (3 equiv) tion of simple sulfides (eq 34)45 and cyclic dithioacetals (eq 35),46
_
MeOH, rt, 6 h
O
using a di-�-oxo (salen) titanium-based catalyst (eq 36).
78%
N
+
O
Ph CH2Ph
catalyst (2 mol %)
S
+
S (34)
Ph Me
UHP (1 equiv)
Ph Me
Aromatic aldoximes are oxidized with UHP and catalytic
MeOH, 0 �C
78%, 98% ee
methyltrioxorhenium, affording the corresponding nitrocom-
pounds.37 Formation of carbamates was observed from
O
2,6-disubstituted aryl oximes, probably via nitrile oxide interme-
S S+
catalyst (2 mol %)
diates (eq 30).37
(35)
Ph Ph
UHP (1 equiv)
S S
MeOH, 0 �C
N
OH Cl
MTO (2 4 mol %) 83%, 92% ee
H
UHP (3 equiv)
N OMe
Cl Cl (30)
MeOH
64% O
Cl
H
Cl
N N
Ti
Secondary amines were oxidized to nitrones using urea
O O
Cl H2O, Et3N
hydrogen peroxide in combination with several metal catalysts, in-
Ph Ph
CH2Cl2
cluding Na2WO4, Na2MoO4, SeO2,38 or MeReO3 (MTO).39 This
latter procedure was optimized, reducing the quantity of MTO up
catalyst
(36)
to 0.5 mol % on a 10 g scale (eq 31).40
m/z = 1778.55
MTO (0.5%)
N
The metal- and solvent-free solid-state oxidation protocol with
H
UHP (3 equiv)
UHP developed for N-oxidation of heteroaromatic azines was also
MeOH
94%
applied to the chemoselective oxidation of sulfides to sulfoxides
(eq 37).34
N+
(31)
_
O
O
+
SMe S
UHP (2 equiv)
Me
The conversion of tungsten-silanes into tungsten silanols in
(37)
15 min
the presence of catalytic MTO and UHP was observed.41 The
80%
MTO/UHP system is able to oxidize triorganosilanes to the cor-
responding silanols: it was proposed that the transfer of oxygen
The cetylpyridinium dodecatungstate on fluoroapatite (FAp)
takes place in helical urea channels, the urea matrix serving as
catalyst applied to the solvent free-epoxidations of olefins was
host for the silane substrate, the H2O2 oxygen source, and the
also used for the chemoselective conversion of sulfides into
metal catalyst.42 In the confined environment of the urea helical
sulfoxides with a slight excess of UHP.31 When 2.5 equiv of UHP
channels, the metal catalyst is stabilized against decomposition,
are used, the selective formation of sulfones is observed.47
while condensation to disiloxane (B), favored in 85% aq H2O2, is
Microporous molecular sieves such as titanium silicates (TS-1
avoided for steric reasons (eq 32). Enantiomerically pure silanes
and TS-2) were employed as catalysts in the oxidation of sulfides.
were oxidized with very high stereoselectivity.42
Crystalline microporous titanium silicate 1 (TS-1) has a pore size
of 5.5 �, which limits its applications to small molecules able to
MTO (1 mol %)
enter the channels and reach the active site. A Ti-beta with larger
Et
Ox (1 equiv) Et Et
pores (6.5 �) allowed the oxidation of bulkier sulfides (eq 38).48
Me Si H + (32)
Me Si OH Me Si O
CH2Cl2, rt, 18 h
Me
Me Me
2
UHP/Ti-beta
A B
S acetone
Ox = UHP 94% 6%
20 �C, 2 h
94%
Ox = 85% H2O2 <5% >95%
O
The chemoselective oxidation of sulfides to sulfoxides was (38)
S
achieved with UHP in the presence of (Ph3P)2ReOCl3 as catalyst.
Avoid Skin Contact with All Reagents
6 HYDROGEN PEROXIDE UREA
Finally, the synthesis of symmetrical disulfides was carried out Baeyer Villiger oxidation. The lactone thus formed undergoes
by oxidation of aromatic thiols with urea hydrogen peroxide and a lipase-mediated perhydrolysis to peroxy-acids which effect
ć%
Mn(III)-salen complex under mild conditions (MeOH, 0 C, 5 30 autocatalytic Baeyer Villiger oxidation. This method represents
min).49 an attractive alternative to the existing procedures for the in situ
generation of peroxycarboxylic acids. Anhydrous UHP allowed
Other Reactions. Aromatic aldehydes bearing an electron- high conversions, while aqueous hydrogen peroxide failed.
donating substituent either in ortho or para position to the
O
O
carbonyl group can be converted into the corresponding
CH3 Novozym SP 435
phenols (Dakin reaction) using UHP in combination with mag- O
(42)
nesium monoperoxyphthalate or acetic anhydride.50 The oxida- UHP, 90 h, 25 �C
CH3
90% conv.
tion of hydroxylated aldehydes and ketones to polyphenols could
also be carried out with urea hydrogen peroxide in the solid state
The MTO-catalyzed conversion of several differently subs-
ć%
55 85 C (eq 39).34
tituted furans to enediones was achieved with UHP in dichloro-
methane.58 Furans containing a hydroxymethyl group at the
CHO
OH
UHP (2 equiv)
2-position, e.g., methylfurfuryl alcohols, were oxidized in high
(39)
85 �C, 20 min
yield to substituted pyranones (eq 43).
OH
OH
80%
O
On the contrary, aromatic aldehydes are oxidized to the
MTO (5 mol %)
corresponding benzoic acid derivatives by the hydroperoxide
(43)
anion generated from UHP or aqueous hydrogen peroxide,50 or UHP (1.2 equiv) O
O
CH2Cl2, rt
OH
in formic acid.51
OH
Several eco-friendly solvent-free systems for the oxidation of
A tandem catalytic process involving an oxazidiridine and
aromatic compounds were developed. Halogenations of arenes
3,5-bis(trifluoromethyl)benzeneseleninic acid, both formed in situ
were carried out using UHP as the oxidant. Molecular iodine with
ć%
by reaction of a bis(3,5-bis(trifluoromethyl)phenyl)-diselenide
a twofold amount of arene and UHP in ethyl acetate at 45 55 C
with hydrogen peroxide (eq 44).59 While aqueous hydrogen per-
for 1 3 h afforded the monoiodo derivatives in good yields.52
oxide was ineffective, the benzeneseleninic acid reagent enabled
A solid-state oxidation of iodoarenes to (dichloroiodo)arenes was
hydroxylation of unactivated tertiary C H bonds using urea hy-
also described, with 2 equiv of UHP and an excess of hydrochloric
acid.53 Finally, benzylic oxidation was afforded using urea drogen peroxide as the terminal oxidant (eq 45).59 This protocol
also allows high yielding Baeyer Villiger oxidations (eq 46) and
hydrogen peroxide under microwave irradiation (eq 40).54
epoxidations (eq 47), of relatively unreactive terminal alkenes.
COOH
F3C
O
O
UHP (15 equiv)
Cl
(40) S
Se
H2O
MW, 150 �C, 180 s SOx
O
O OH N
75%
F3C F3C
I
(44)
The oxidative carbon carbon cleavage of aryl ketones to
F3C
aromatic carboxylic acids was afforded using [hydroxy(2,4-
O Sred
H2O2 O
Cl
dinitrobenzenesulfonyloxy)iodo]benzene followed by UHP in the
Se
S
ionic liquid [bmim]BF4 (eq 41).55 Efficient chlorination of aryl O
N
OH
F3C
F3C
O
ketones to ą-chloroketones with aluminum chloride hexahydrate
and UHP was also achieved in [bmim]BF4 (eq 41).56
bis(3,5-bis(trifluoromethyl)phenyl)
H
OH
-diselenide (1 mol %)
NO2
imine I (20 mol %)
OH O
(45)
O
UHP (4 equiv)
Ph I O S NO2
dichloroethane
H
H
O
OH
35 �C, 48 h
63%
[bmim]BF4, UHP
85% bis(3,5-bis(trifluoromethyl)phenyl)
OH
O
O
-diselenide (1 mol %)
(41)
imine I (20 mol %)
O
O
(46)
UHP (4 equiv)
Cl
AlCl3�6H2O dichloroethane
22 �C, 72 h
70%
[bmim]BF4, UHP
77%
bis(3,5-bis(trifluoromethyl)phenyl)
-diselenide (1 mol %)
imine I (10 mol %)
The oxidation of cyclic ketones to lactones (Baeyer Villiger
OBz
oxidation) by peroxycarboxylic acids is well known. A very mild
UHP (2 equiv)
dichloroethane
procedure for the autocatalytic Baeyer Villiger oxidation using
rt, 36 h O
lipases was developed (eq 42).57 Hydrogen peroxide, assisted
(47)
OBz
by the protein side chain carboxylic groups, was able to induce
A list of General Abbreviations appears on the front Endpapers
HYDROGEN PEROXIDE UREA 7
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OCOCF3
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