CHROMIUM(VI) OXIDE

1

Chromium(VI) Oxide

1

CrO

3

[1333-82-0]

CrO

3

(MW 99.99)

InChI = 1/Cr.3O/rCrO3/c2-1(3)4
InChIKey = WGLPBDUCMAPZCE-YFSAMUSXAF

(reagent for oxidizing carbon–hydrogen bonds to alcohols,
oxidizing alkylaromatics to ketones and carboxylic acids, convert-
ing alkenes to α,β-unsaturated ketones, oxidizing carbon–carbon
double bonds, oxidizing arenes to quinones, oxidizing alcohols

to aldehydes, ketones, acids, and keto acids)

Alternate Names:

chromic anhydride; Chromic Acid in aqueous

media.

Physical Data:

mp 196

◦

C; d 2.70 g cm

−3

.

Solubility:

sol ether, H

2

O, HNO

3

, H

2

SO

4

, DMF, HMPA.

Form Supplied in:

red crystals.

Handling, Storage, and Precautions: caution

: chromium(VI) ox-

ide is a highly toxic cancer suspect agent. All chromium(VI)
reagents must be handled with care. The mutagenicity of Cr

VI

compounds is well documented.

7

HMPA is also a highly toxic

cancer suspect agent. Special care must always be exercised in
adding CrO

3

to organic solvents. Add CrO

3

in small portions to

HMPA in order to avoid a violent decomposition. This reagent
must be handled in a fume hood.

Each mol of chromium(VI) oxide has 1.5 equivalents of

oxygen. The oxidizing power of the reagent increases with
decreasing water content of the solvent medium. The oxidizing
medium may be aqueous acetic acid,

2,3

anhydrous acetic acid

(Fieser reagent),

4

or concentrated

5

or aqueous

6

sulfuric acid.

Original Commentary

Fillmore Freeman
University of California, Irvine, CA, USA

Oxidation of Carbon–Hydrogen Bonds to Alcohols.

Chromium(VI) oxide in 91% acetic acid oxidizes the methine
hydrogen of (+)-3-methylheptane to (+)-3-methyl-3-heptanol
with 70–85% retention of configuration.

8

3β-Acetoxy-14α-

hydroxyandrost-5-en-17-one is obtained by direct introduc-
tion of an α-hydroxyl group at C-14 in the dibromide of
3β-acetoxyandrost-5-en-17-one (eq 1).

9

AcO

H

O

AcO

OH

O

1. Br

2

2. CrO

3

, AcOH

(1)

3. Zn

44%

Oxidation of Alkylaromatics to Ketones and Carboxylic

Acids.

Chromium(VI) oxide in concentrated sulfuric acid

oxidizes 3,4-dinitrotoluene to 3,4-dinitrobenzoic acid (89%).

5

Under milder conditions, with longer alkyl chains, the benzylic
position is converted to carbonyl. Chromium(VI) oxide in acetic
acid oxidizes ethylbenzene to acetophenone and benzoic acid.
More rigorous oxidizing experimental conditions convert longer
chain alkyl groups to carboxyl, thus yielding benzoic acid or its
derivatives. Methylene groups between two benzene rings are
oxidized to carbonyl derivatives in preference to reaction at alkyl
side chains.

10

Indanes are oxidized to 1-indanones by use of a

dilute (10%) solution of chromium(VI) oxide in acetic acid at
room temperature (eq 2).

11

CrO

3

, AcOH

(2)

R

1

R

R

1

R

O

87–92%

Allylic Oxidations.

Allylic oxidations may be compli-

cated by carbonyl formation at either one or both allylic
positions. Although chromium(VI) oxide appears to be use-
ful for allylic oxidation in steroid chemistry, better results
may be obtained in other systems with Di-tert-butyl Chro-
mate or Dipyridine Chromium(VI) Oxide (Collins reagent).
However,

the

Chromium(VI)

Oxide–3,5-Dimethylpyrazole

complex (CrO

3

·DMP) is useful for allylic oxidations. The

complex oxidized the allylic methylene group in (1) to the
α

,β-unsaturated ketone (2) which was used in the synthesis

of the antibacterial helenanolide (+)-carpesiolin (eq 3).

12

Chromium(VI) oxide in glacial acetic acid oxidizes 3,21-
diacetoxy-4,4,14-trimethyl-

8

-5-pregnene

to

the

enetrione

(eq 4).

13

Complex product mixtures are formed when epoxida-

tion competes with the allylic oxidation.

14

(1)

H

O

O

H

CrO

3

·DMP

CH

2

Cl

2

O

O

(2)

O

(3)

60%

AcO

O

OAc

AcO

O

OAc

O

CrO

3

, AcOH

O

(4)

75%

Oxidation of Carbon–Carbon Double Bonds.

Chro-

mium(VI) oxide in aqueous sulfuric acid generally cleaves
carbon–carbon double bonds. Rearrangements may further com-
plicate the oxidation. In anhydrous acetic acid, chromium(VI)
oxide oxidizes tetraphenylethylene to the oxirane (70% yield) and
benzophenone (11%).

15

The yield is lower and more double bond

cleavage occurs in aqueous acetic acid. However, use of acetic
anhydride as solvent (see Chromyl Acetate) affords the oxiranes
from tri- and tetrasubstituted alkenes in 50–88% yields, along with
benzopinacols.

16,17

Many steroidal and terpenic cyclic alkenes

react with chromium(VI) oxide in acetic acid to give oxiranes,

Avoid Skin Contact with All Reagents

2

CHROMIUM(VI) OXIDE

and saturated, α,β-unsaturated, α-hydroxy, and α,β-epoxy ketones
which arise from the initially formed oxirane.

18,19

A synthetically

useful cleavage of double bonds involving chromium(VI) oxide
is the Meystre–Miescher–Wettstein degradation

20

which short-

ens the side chain of a carboxylic acid by three atoms at one
time. This procedure is a modification of the Barbier–Wieland
degradation.

21,22

Oxidation of Arenes to Quinones.

In contrast to alky-

laromatics, which undergo oxidation at the side chain with
some chromium(VI) oxidants, polynuclear aromatic arenes un-
dergo ring oxidation to quinones with chromium(VI) oxide.
This chemoselectivity is shown in the chromium(VI) oxide
in anhydrous acetic acid (Fieser reagent) oxidation of 2,3-
dimethylnaphthalene to 2,3-dimethylnaphthoquinone in quanti-
tative yield (eq 5).

23

In some cases, depending on experimental

conditions, both benzylic and ring oxidations occur

24

or the alkyl

groups may be eliminated (eq 6).

25

The oxidation of anthracene

derivatives is important in the total synthesis of anthracycline
antibiotics.

26,27

CrO

3

, AcOH

(5)

O

O

100%

CrO

3

, AcOH

(6)

O

O

Et

Oxidation of Alcohols to Aldehydes, Ketones, Acids, and

Keto Acids. Chromium(VI) oxide in acetic acid oxidizes pri-
mary alcohols to aldehydes and acids, and secondary alcohols
to ketones and keto acids (Fieser reagent) (eq 7).

28

Chromium(VI)

oxide in water or aqueous acetic acid oxidizes primary alcohols
to carboxylic acids.

29,30

Chromium(VI) oxide–Hexamethylphos-

phoric Triamide (CrO

3

·HMPA) selectively oxidized the primary

hydroxyl group of strophanthidol (3) to an aldehyde group in the
final step in the synthesis of strophanthidin (4) (eq 8).

31

The

CrO

3

·HMPA complex oxidizes saturated primary alcohols to

aldehydes in about 80% yield.

32,33

The yields are lower with sec-

ondary alcohols and highest with α,β-unsaturated primary and
secondary alcohols. It is possible to selectively oxidize certain
allylic and benzylic hydroxyl groups in the presence of other
unprotected saturated groups (eq 9; cf eq 8). Chromium(VI) ox-
ide in DMF in the presence of catalytic amounts of sulfuric acid
oxidizes steroidal alcohols to ketones.

34

Chromium(VI) oxide on

graphite selectively oxidizes primary alcohols in the presence of
secondary and tertiary alcohols.

35

CrO

3

, AcOH

(7)

OH

Ph

CO

2

H

O

Ph

81%

HO

OH

HO

O

O

HO

OH

O

O

O

(8)

CrO

3

·HMPA

(3)

(4)

35%

CrO

3

·HMPA

(9)

HO

OH

HO

O

80%

Other Applications. Chromium(VI) oxide in aqueous acetic

acid converts α-chlorohydrindene to α-hydrindanone (50–60%).

36

Suitably protected methylene or benzylidene acetals of alditols are
cleaved by chromium(VI) oxide in glacial acetic acid to deriva-
tives of ketoses.

37

Chromium(VI) oxide in anhydrous acetic acid

converts methyl ethers into the corresponding formates, which can
be hydrolyzed by base to alcohols (demethylation).

38

First Update

Seongmin Lee
Purdue University, West Lafayette, IN, USA

Oxidation of Alcohols. Catalytic chromium(VI) oxide (1.2

mol %) together with 2.5 equiv of periodic acid as co-oxidant
in wet acetonitrile converts various primary alcohols to the car-
boxylic acids in excellent yields (eq 10).

39

Notably, chiral alcohols

are cleanly oxidized to carboxylic acids without racemization at
the adjacent chiral centers (eq 11). Cr

VI

-catalyzed oxidation of

secondary alcohols give the corresponding ketones in a nearly
quantitative yield (eq 12). No product formation was observed in
the absence of chromium(VI) oxide or when acetone was used as
solvent.

Br

OMe

OH

CO

2

H

Br

OMe

CrO

3

(1.2 mol %)

H

5

IO

6

(2.5 equiv)

CH

3

CN, 0

°C, 1 h

95%

(10)

N

O

O

Ph

HO

N

O

O

HO

2

C

Ph

CrO

3

(1.2 mol

%)

H

5

IO

6

(2.5 equiv)

CH

3

CN, 0

°C, 1 h

73%

(11)

OH

O

CrO

3

(1.2 mol

%)

H

5

IO

6

(2.5 equiv)

CH

3

CN, 0

°C, 1 h

98%

(12)

A list of General Abbreviations appears on the front Endpapers

CHROMIUM(VI) OXIDE

3

Benzylic Oxidation. Chromium(VI) oxide acts as an efficient

catalyst for the benzylic oxidation with periodic acid as the termi-
nal oxidant in acetonitrile at 25

◦

C. Various substituted toluenes

are converted to the corresponding benzoic acids (eq 13).

40

Cyclic

benzyl ethers are oxidized to the lactones in excellent yields.

40

Isochroman is oxidized to 3,4-dihydroisocoumarin quantitatively
by using 2 equiv of periodic acid and 1 mol % of chromium(VI)
oxide (eq 14). 4-Ethyl-3-nitro-benzoic acid is efficiently trans-
formed into 4-acetyl-3-nitro-benzoic acid by 3 mol % chro-
mium(VI) oxide and periodic acid.

41

NC

CO

2

H

NC

CrO

3

(20 mol %)

H

5

IO

6

(3.5 equiv)

CH

3

CN, 25

°C

84%

(13)

O

O

O

CrO

3

(1 mol

%)

H

5

IO

6

(2 equiv)

CH

3

CN, 25

°C, 10 min

99%

(14)

Oxidation of Arenes to Quinones. Chromium(VI) oxide cat-

alyzes the oxidation of arenes to the corresponding quinones with
excess periodic acid in good to excellent yield.

42

2-Methylnapht-

halene is smoothly converted to 2-methyl-1,4-naphthoquione
(vitamin K

3

) at 5

◦

C in the presence of 10 mol % of chromium(VI)

oxide and 4.2 equiv of periodic acid (eq 15). 1,3,5-Trimethoxyben-
zene is transformed into 2,6-dimethoxy-1,4-benzoquinone in 90%
yield with 3 mol % catalyst (eq 16).

O

O

CrO

3

(10 mol %)

H

5

IO

6

(4.2 equiv)

CH

3

CN, 5

°C, 1 h

61%

vitamin K

3

(15)

MeO

OMe

OMe

OMe

MeO

O

O

CrO

3

(3 mol %)

H

5

IO

6

(5 equiv)

CH

3

CN, 5

°C, 1 h

90%

(16)

Oxidation of Sulfides to Sulfones.

Chromium(VI) oxide/

periodic acid is an excellent catalytic system for the oxida-
tion of sulfides to sulfones.

43

A myriad of electron-rich and

electron-deficient sulfides are oxidized to sulfones with 2 mol %
chromium(VI) oxide and 2 equiv periodic acid at low tempera-
ture (eq 17). Higher catalyst loading (10 mol %) led to shorter
reaction time and a highly chemoselective oxidation of sulfides
to sulfones in the presence of readily oxidized functional groups.
Both carbon-carbon double bonds and triple bonds are unaffected
by this catalytic system. Sulfides containing phenol, primary al-
cohol, and aldehyde are converted to the corresponding sulfones
(eq 18). However, benzylic alcohol and secondary alcohol moi-
eties are not tolerated under the oxidation conditions and give very
poor yields of the desired sulfones due to competing oxidation of

hydroxyl group. Amide and heterocyclic nitrogen atoms are not
affected by the oxidation condition.

F

S CF

3

F

S

O

CF

3

O

MeCN, 25

°C, 2.5 h

96%

CrO

3

(2 mol

%)

H

5

IO

6

(4 equiv)

(17)

HO

S

CH

3

HO

S

CH

3

O

O

CrO

3

(10 mol

%)

H

5

IO

6

(2.1 equiv)

MeCN/EtOAc

−35

°C, 1 h

94%

(18)

Direct Functionalization of C–H Bonds.

Stoichiometric

chromium(VI) oxide (3 equiv) together with tetrabutylammo-
nium periodate (3 equiv) efficiently oxyfunctionalizes C–H bonds
of various activated and nonactivated hydrocarbons. It oxidizes
steroidal cyclic ethers to the corresponding hydroxylated cyclic
ethers.

43

It is proposed that a monoperoxo Cr

VI

species struc-

turally similar to the dioxiranes, is generated in situ by the re-
action of chromium(VI) oxide with Bu

4

NIO

4

and serves as the

active C–H oxidant. The generated oxidant is stable at −40

◦

C

and has an orange color typical of Cr

VI

.

The value of this oxidation is its extremely mild conditions

combined with selectivity. The Cr

VI

-mediated C–H oxidations

occur at about −40

◦

C and are typically complete within 10 min.

The observed retention of configuration strongly suggests that the
C–H oxidation proceeds through a concerted “three-center two-
electron” oxenoid insertion into C–H bonds rather than through
radical intermediates.

Several impressive oxyfunctionalization reactions on steroid

substrates illustrate the scope of this process. Oxidation-
susceptible olefin and iodide moieties, which ultimately give
epoxides under the influence of dimethyldioxirane or m-CPBA,
are unreactive under these oxidation conditions, highlighting the
chemoselectivity of the Cr-mediated C–H oxidation. The unusual
chemoselectivity for C–H oxidation over epoxidation is in keep-
ing with a theoretical study that Cr

VI

peroxo species have higher

calculated activation barriers for oxygen transfer to ethylene; they
are less prone to epoxidation than similar Mo

VI

and W

VI

species.

The C–H bond at either C16 (eq 19) or C22 (eq 20) in steroid

cyclic ethers is oxidized in excellent yield to give the correspond-
ing hemiacetals as a function of their electronic environments.

44

AcO

BzO

O

BzO

AcO

OBz

O

OH

BzO

CrO

3

(3 equiv)

Bu

4

NIO

4

(3 equiv)

MeCN/MC (3:1)

−40

°C, 10 min

75%

16

(19)

22

Avoid Skin Contact with All Reagents

4

CHROMIUM(VI) OXIDE

AcO

BzO

O

OAc

OBz

AcO

BzO

O

OAc

OBz

OH

22

CrO

3

(3 equiv)

Bu

4

NIO

4

(3 equiv)

MeCN/MC (3:1)

−40

°C, 10 min

69%

(20)

The regioselectivity of these C–H oxidations is illustrated in the

oxidation of bistetrahydrofuran. Out of many potential products,
C16 hemiacetal is obtained as the major product (eq 21).

AcO

OAc

O

O

AcO

OAc

O

O

OH

CrO

3

(3 equiv)

Bu

4

NIO

4

(3 equiv)

MeCN/MC (3:1)

−40

°C, 10 min

62%

(21)

A diketone is obtained in 84% yield via the bishemiacetal

intermediate from the oxidation of E-ring tetrahydrofuran at an
elevated reaction temperature (eq 22). The absence of epimeriza-
tion α to carbonyl illustrates the mildness of this oxidation.

AcO

O

O

AcO

O

O

O

O

O Cr

O

O

OH

O

O Cr

O

O

OH

O

HO Cr

O OH

O

[O]

CrO

3

(3 equiv)

Bu

4

NIO

4

(3 equiv)

MeCN/MC (3:1)

−40

°C, 10 min

79%

(23)

AcO

AcO

O

OAc

AcO

AcO

AcO

OAc

AcO

O

O

CrO

3

(5 equiv)

Bu

4

NIO

4

(5 equiv)

MeCN/MC (3:1)

−20

°C, 2 h

84%

(22)

In the case of an E-ring cyclic enol ether, an allylic oxidation

product is obtained, presumably via sequential enol ether attack
on Cr

VI

species, [3,3]-sigmatropic rearrangement, and allylic

oxidation (eq 23).

Substrates for chromium(VI) oxide/Bu

4

NIO

4

-mediated C–H

oxidation are not limited to steroidal cyclic ethers. C–H bonds
of nonactivated hydrocarbons are readily oxidized to give tertiary
alcohol or ketone.

The sterically less hindered tertiary C–H bond of a menthol

derivative has been oxidized preferentially over secondary ben-
zylic position also adjacent to oxygen, the tertiary α position of
the acyclic ether, and the sterically more hindered tertiary C–H
bonds (eq 24).

44

The C–H oxidation is stereospecific with the retention of stereo-

chemistry of the C–H bond oxidized. So the oxidation of cis-
decalin results in the formation of cis-decanol (eq 25).

Preference of tertiary C–H bond over secondary is seen in the

oxidation of adamantane (eq 26). Secondary C–H bonds are also
oxidized to give the corresponding ketones. Cyclohexane is oxi-
dized to cyclohexanone, but the reaction requires an elevated re-
action temperature and prolonged reaction time (eq 27).

A list of General Abbreviations appears on the front Endpapers

CHROMIUM(VI) OXIDE

5

O

O

OH

CrO

3

(3 equiv)

Bu

4

NIO

4

(3 equiv)

MeCN/MC (3:1)

−40

°C, 10 min

76%

(24)

H

H

OH

H

CrO

3

(3 equiv)

Bu

4

NIO

4

(3 equiv)

MeCN/MC (3:1)

−40

°C, 10 min

84%

(25)

OH

CrO

3

(3 equiv)

Bu

4

NIO

4

(3 equiv)

MeCN/CH

2

Cl

2

(3:1)

−40

°C, 10 min

55%

(26)

O

MeCN/MC (3:1)

−20

°C, 1 h

57%

(27)

CrO

3

(3 equiv)

Bu

4

NIO

4

(3 equiv)

Second Update

Hong Shu & Mark Trudell
University of New Orleans, New Orleans, LA, USA

Oxidation of N-alkylamides to Imides.

Chromium(VI)

oxide catalyzed periodic acid oxidation converted a large variety
of N-alkylbenzamides and N-alkylamides into the corresponding
imides in good to excellent yields.

45

Acetonitrile was used as the

solvent and the presence of acetic anhydride was required to re-
duce the N-dealkylation side-reaction caused by moisture in the
reaction mixture. The oxidation went smoothly at −10

◦

C to room

temperature with low catalyst loading (1.0–2.5 mol%).

The reaction selectively oxidized N-alkylbenzamides and N-

alkylamides, exhibiting good tolerance for a variety of func-
tional groups. An N-propargylbenzamide was chemoselectively
oxidized without affecting the carbon–carbon triple bond (eq 28).
No competitive hydroxylation of the tertiary C–H was observed
in the oxidation of N-isobutylbenzamide (eq 29). The carbonyl
group of N-benzylformamide (eq 30) and the carbon–carbon dou-
ble bond of N-benzylacrylamide (eq 31) were compatible with the
reaction conditions.

45

N
H

O

N
H

O

O

H

5

IO

6

(6 equiv)

Ac

2

O (6 equiv)

CrO

3

(10 mol %)

(28)

CH

3

CN, 0

°C

90%

N
H

O

H

N
H

O

O

H

H

5

IO

6

(6 equiv)

Ac

2

O (6 equiv)

CrO

3

(5 mol %)

(29)

CH

3

CN, 0

°C

87%

H

N
H

O

N
H

O

O

H

H

5

IO

6

(6 equiv)

Ac

2

O (6 equiv)

CrO

3

(2.5 mol %)

(30)

CH

3

CN, 0

°C

92%

N
H

O

N
H

O

O

H

5

IO

6

(6 equiv)

Ac

2

O (6 equiv)

CrO

3

(5 mol %)

(31)

CH

3

CN, 0

°C

88%

Oxidation of Benzylic Alcohols and TBDMS Ethers. Cat-

alytic chromium(VI) oxide with periodic acid in CH

3

CN/CH

2

Cl

2

at low temperature (−78

◦

C) selectively oxidized benzylic alco-

hols to aldehydes or ketones (eq 32). The mild conditions also
provided a one-pot transformation of benzylic TBDMS ethers into
aldehydes and ketones (eq 33).

46

At low temperature, this method

is highly selective for TBDMS-protected benzylic alcohols over
benzylic alcohols protected by other traditional hydroxyl protect-
ing groups (TBDPS, BOC, or MOM).

46

OH

HO

H

HO

O

CrO

3

(1 mol %)

H

5

IO

6

(2 equiv)

CH

3

CN:CH

2

Cl

2

(1:1)

–78

°C, 1 h

(32)

91%

OTBDMS

TBDPSO

H

O

TBDPSO

CrO

3

(1 mol %)

H

5

IO

6

(3 equiv)

CH

3

CN:CH

2

Cl

2

(1:1)

–78

°C, 1 h

(33)

90%

Oxidation of N-Alkyl-o-methyl-arenesulfonamides to Sac-

charin Derevatives.

1,2-Benzisothiazole-3-one-1,1-dioxides

(saccharins) can be prepared by chromium(VI) oxide catalyzed
periodic oxidation.

47

Employing 8 equiv of periodic acid,

10 mol % of CrO

3

, and 8 equiv of acetic anhydride in acetonitrile,

N

-tert-butyl-6-bromo-o-toluenesulfonamide was successfully ox-

idized to N-tert-butyl-6-bromosaccharin in a 90% yield (eq 34).

47

S

CH

3

N
H

O

O

Br

S

O

O

Br

N

O

H

5

IO

6

(8 equiv)

Ac

2

O (8 equiv)

CrO

3

(10 mol %)

90%

(34)

CH

3

CN, rt, 8 h

Related

Reagents. Chromium(VI)

Oxide–3,5-dimethyl-

pyrazole;

Chromium(VI)

Oxide–Quinoline;

Chromium(VI)

Oxide–Silica Gel; Dimethyldioxirane; Methyl(trifluoromethyl)
Dioxirane; Chromylacetate.

1.

(a) Wiberg, K. B., Oxidation in Organic Chemistry; Wiberg, K. B., Ed.;
Academic: New York, 1965; Part A, p 131. (b) Freeman, F., Organic
Synthesis By Oxidation With Metal Compounds

; Miijs, W. J.; de Jonge,

C. R. H. I., Eds.; Plenum: New York, 1986; Chapter 2. (c) Lee, D. G., The
Oxidation of Organic Compounds by Permanganate Ion and Hexavalent
Chromium

; Open Court: La Salle, IL, 1980. (d) Stewart, R., Oxidation

Avoid Skin Contact with All Reagents

6

CHROMIUM(VI) OXIDE

Mechanisms: Applications to Organic Chemistry

; Benjamin: New York,

1964. (e) Cainelli, G.; Cardillo, G., Chromium Oxidations in Organic
Chemistry

; Springer: Berlin, 1984.

2.

Schreiber, J.; Eschenmoser, A., Helv. Chim. Acta 1955, 38, 1529.

3.

Braude, E. A.; Fawcett, J. S., Org. Synth., Coll. Vol. 1963, 4, 698.

4.

Nakanishi, K.; Fieser, L. F., J. Am. Chem. Soc. 1952, 74, 3910.

5.

Borel, E.; Deuel, H., Helv. Chim. Acta 1953, 36, 801.

6.

Kuhn, R.; Roth, H., Chem. Ber. 1933, 66, 1274.

7.

Cupo, D. Y.; Wetterhahn, K. E., Cancer Res. 1985, 45, 1146.

8.

Wiberg, K. B.; Foster, G., J. Am. Chem. Soc. 1961, 83, 423.

9.

St. André, A. F.; MacPhillamy, H. B.; Nelson, J. A.; Shabica, A. C.;
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A list of General Abbreviations appears on the front Endpapers