A mild and efficient cleavage of gem-Diacetates to aldehydes by CBr4

Article abstract of DOI:10.1081/SCC-100103542

gem-Diacetates are selectively deprotected to the corresponding aldehydes in high yields by CBr₄ in refluxing acetonitrile under neutral reaction conditions.

Full text of DOI:10.1081/SCC-100103542

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A MILD AND EFFICIENT
CLEAVAGE OF gem-
DIACETATES TO ALDEHYDES
*
BY CBr4
a
a
T. Ramalingam , R. Srinivas , B. V. Subba Reddy
a
a
a
&
J. S. Yadav
Organic Chemistry Division-I , Indian Institute of
Chemical Technology , Hyderabad, 500 007, India
Published online: 09 Nov 2006.
To cite this article: T. Ramalingam , R. Srinivas , B. V. Subba Reddy & J. S. Yadav
(
2001) A MILD AND EFFICIENT CLEAVAGE OF gem-DIACETATES TO ALDEHYDES BY CBr4
*
,
Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 31:7, 1091-1095, DOI: 10.1081/SCC-100103542
To link to this article: http://dx.doi.org/10.1081/SCC-100103542
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SYNTHETIC COMMUNICATIONS, 31(7), 1091–1095 (2001)
A MILD AND EFFICIENT CLEAVAGE
OF gem-DIACETATES TO ALDEHYDES
BY CBr4*
y
T. Ramalingam, R. Srinivas, B. V. Subba Reddy, and J. S.
Yadav
Organic Chemistry Division-I, Indian Institute of Chemical
Technology, Hyderabad-500 007, India
ABSTRACT
gem-Diacetates are selectively deprotected to the
corresponding aldehydes in high yields by CBr in refluxing
acetonitrile under neutral reaction conditions.
4
Selective protection and deprotection of carbonyl groups play an
1
important role in the multistep synthesis of complex natural products.
,2
Among various carbonyl protecting groups, gem-diacetates are the most
commonly used due to their stability toward a variety of reaction conditions
and ease of installation/removal under mild conditions. Further, gem-
diacetates are useful intermediates in various transformations, such as
3
,4
5,6
nucleophilic substitution reactions and Diels-Alder reactions. Various
methods are available for the deprotection of diacetates, which include acid-
7
catalyzed cleavage by sulfuric acid, hydrochloric acid, K10 clay, and
8
9
1
BI -N,N-diethylaniline complex, as well as base-catalyzed cleavage by
0
3
*
IICT Communication No. 4491.
Corresponding author.
y
1
091
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

1
092
RAMALINGAM ET AL.
1
sodium hydroxide or aqueous potassium carbonate. Also, the cleavage has
1
1
been achieved by CAN coated on silica gel or by neutral alumina under
2
1
3
microwave irradiation. However, in spite of their potential utility, some of
these methods suffer from drawbacks like longer reaction times, unsatisfac-
tory yields, incompatibility with other protecting/functional groups, and
require strongly acidic or basic conditions.
Consequently, the development of new reagents with more efficacy,
convenient procedures, and better yields is desirable. Although the use
1
4–17
of CBr as catalyst and reagent for various transformations
4
is reported,
it has not been used for the deprotection of gem-diacetates. Herein, we
report a mild and selective method for the deprotection of gem-diacetates
to corresponding aldehydes by CBr in acetonitrile at reflux temperature.
4
The deprotection proceeds smoothly by the treatment of diacetate with a
catalytic amount of CBr in refluxing acetonitrile (Scheme).
4
Scheme.
Thus, a variety of diacetates were deprotected selectively in the
presence of other protecting groups, such as OAc, OBn, O-allyl, OMe,
OBz, BOC, and CBz. Other functional groups (esters, epoxides, THP
ethers, and olefins) are compatible by CBr in refluxing acetonitrile. High
4
chemoselectivity was observed when the reactions were carried out in
acetonitrile. The advantage of the use of CBr in acetonitrile lies in its
4
simplicity. Neither expensive reagents nor overly acidic or basic conditions
are employed. The occurance of this cleavage may be attributed to the in
situ formation of catalytic amount of HBr itself from CBr in refluxing
4
acetonitrile. Aliphatic and ꢀ,ꢁ-unsaturated diacetates were deprotected to
the corresponding aldehydes without any decomposition, which was
generally observed in the deprotection of diacetates by Lewis acids.
Further, gem-diacetates were selectively cleaved to the parent carbonyl
compounds in the presence of phenolic acetate. (Table)
In conclusion, we described a mild and efficient procedure for the
selective deprotection of gem-diacetates to the parent aldehydes using
CBr4 in refluxing acetonitrile. The procedure is simple, selective, and
high-yielding, which provides a useful addition to existing methods.

DL139-CH20-UC1-30
gem-DIACETATES
1093
Table. Selective Cleavage of gem-Diacetates to Aldehydes Catalyzed by CBr
Acetonitrile
4
in
a
b
Entry
a
Substrate
Product
Reaction Time (h) Yield (%)
3
78
b
c
5
4
81
89
d
e
6
5
84
85
f
8
6
73
88
g
h
8
75
i
j
3
3
89
87
k
l
5
4
81
78
m
n
6
83
3
3
87
84
o
a
1
All the products were characterized by H NMR, IR, and mass spectroscopy.
b
Isolated yields after purification.

1
094
RAMALINGAM ET AL.
EXPERIMENTAL
A mixture of aldehyde diacetate (5 mmol) and CBr (1 mmol) (15 mL)
4
was stirred in refluxing acetonitrile for an appropriate time as required
to complete the reaction. After complete conversion as indicated by TLC,
the reaction mass was cooled to room temperature, diluted with water,
and extracted with ether (2Â20 mL). The combined organic layers were
washed with brine, dried over anhydrous Na SO , and concentrated
2
4
in vacuo to yield crude product, which was purified by silica gel column
chromatography to afford pure aldehyde.
ACKNOWLEDGMENTS
BVS thanks CSIR, New Delhi, for the award of fellowship.
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Received in Japan April 7, 2000