Selective regeneration of carbonyl compounds from oximes with N-bromosuccinimide under neutral and mild conditions

Article abstract of DOI:10.1007/PL00010116

N-Bromosuccinimide has been found to be an efficient and selective reagent for the mild oxidative cleavage of oximes to yield their corresponding carbonyl compounds in good to excellent yields.

Full text of DOI:10.1007/PL00010116

Monatshefte f uÈ r Chemie 129, 1057±1060 (1998)
Selective Regeneration of Carbonyl Compounds
from Oximes with N-Bromosuccinimide Under
Neutral and Mild Conditions
Ã
Babasaheb P. Bandgar , Ramesh R. Kale, and Lalita B. Kunde
Organic Chemistry Research Laboratory, School of Chemical Sciences, Swami Ramanand Teerth
Marathwada University, Nanded-431602, India
Summary. N-Bromosuccinimide has been found to be an ef®cient and selective reagent for the mild
oxidative cleavage of oximes to yield their corresponding carbonyl compounds in good to excellent
yields.
Keywords. Carbonyl compounds; Deoximation; N-bromosuccinimide; Oximes.
Selektive Regenerierung von Carbonylverbindungen aus Oximen mit N-Bromsuccinimid
unter milden neutralen Bedingungen
Zusammenfassung. N-Bromsuccinimid ist ein ef®zientes und selektives Reagens zur milden
oxidativen Spaltung von Oximen. Die entsprechenden Carbonylverbindungen werden in guten bis
ausgezeichneten Ausbeuten erhalten.
Introduction
There has been considerable interest in the development of mild methods for the
regeneration of carbonyl compounds from stable and readily prepared oximes and
tosylhydrazones [1] due to the fact that such derivatives of carbonyl compounds
serve as ef®cient protecting groups for aldehydes and ketones in organic synthesis
[2]. Moreover, since oximes can be prepared from non-carbonyl compounds [3],
the regenerated carbonyl compounds from oximes provide an alternative method
for the preparation of aldehydes and ketones. Most of the known methods of
regenerating carbonyl compounds from their nitrogen derivatives require strongly
acidic [4], oxidative [5], or reductive [6] conditions. Recently, clay supported ferric
nitrate [7], dimethyl dioxirane [8], pyridinium dichromate-t-butyl hydroperoxide
[9], iodosobenzene diacetate [10], the titanium silicalite-1-H O combination [11],
and 70% TBHP [12] have been reported to cleave the C=N bond of oximes and
2 2
tosylhydrazones. However, many of the conventional procedures for regeneration
à Corresponding author

1058
B. P. Bandgar et al.
of the carbonyl function from such nitrogen derivatives have several limitations:
some of the reagents are hazardous or very toxic, expensive, or not readily
available, or they need to be freshly prepared and the reactions require drastic
conditions, long reaction times, and tedious work-up. It is important that most of
the reported methods are suitable for the regeneration of ketones from their oximes
and tosylhydrazones and not for aldehydes where the yields are low due to the
overoxidation of regenerated aldehydes to acids. Therefore, it is desirable that a
method which involves relatively mild reaction conditions should be available,
leading to high recoveries of a wide range of aldehydes and ketones. We now report
an ef®cient and general method for the effective and selective cleavage of oximes
with N-Bromosuccinimide (NBS) under neutral and mild conditions.
Results and Discussion
Dissolution of oximes in acetone with addition of a small amount of water and
ꢀ
subsequent reaction with NBS under stirring at room temperature (25 C) or re¯ux
gave the corresponding carbonyl compounds in good yields. Table 1 summarizes
the results of various oximes which underwent oxidative cleavage with NBS to
form the corresponding carbonyl compounds. The rate of oxidative cleavage of
4
(
-bromobenzophenone oxime was fast. Even the sterically hindered ketone oximes
entries 12±13) were successfully oxidatively cleaved to the corresponding ketones
in good yields. The unsaturated cinnamaldoxime (entry 2), however, was ®rst
brominated at the C=C double bond followed by deoximation. The most remark-
able advantage of this methodology is that it is a general method for oxidative
cleavege of a variety of aldoximes and ketone oximes with NBS under neutral and
mild conditions, and no trace of acid was formed due to overoxidation of the
regenerated aldehyde.
This procedure is also useful for the chemoselective oxidative deoximation
of ketone oximes in the presence of aldoximes. Thus, when equimolar mixtures
of 3-nitrobenzaldoxime and cyclopentanone oxime, 2-nitrobenzaldoxime and
acetophenone oxime, or salicylaldoxime and 4-bromobenzophenone oxime in
ꢀ
acetone and water were allowed to react with NBS as room temperatures (25 C)
for a period of 2.5 h, 3.2 h, and 0.5 h, respectively, the ketone oximes cyclo-
pentanone oxime, acetophenone oxime, and 4-bromobenzophenone oxime under-
went chemoselctively oxidative deoximation giving 65% cyclopentanone, 71%
acetophenone, and 85% 4-bromobenzophenone, whereas the aldoximes 3-
nitrobenzaldoxime, 2-nitrobenzaldoxime, and salicylaldoxime were recovered
unchanged.
In conclusion, we hope that the presented deprotection and deoximation
methodology of oximes will ®nd wide application in organic synthesis because of
the simplicity of work-up and the use of the readily available oxidant NBS under
neutral and mild conditions.

Mild Cleavage of Oximes
1059
Table 1. Oxidative cleavage of oximes with NBS
a
Yield (%)
Entry Substrate
Reaction
Product
conditions
Temp. Time
ꢀ
(
C)
(h)
1
2
60
25
1
95
b
5
70
3
4
25
25
2.5
5
65
88
5
25
3.5
60
6
7
60
25
5
85
88
1.2
8
9
25
25
25
4.3
2.5
3.2
48
67
75
1
1
1
0
1
2
25
25
0.5
1.5
86
87
13
25
1.5
84
a
b
isolated yields; requires 4 equivalents of NBS
Experimental
General procedure
A mixture of the oxime (3 mmol) and NBS (3.1 mmol) in acetone (10 ml) and water (1 ml) was stirred
at the temperature given in Table 1 for the speci®ed time. After the reaction was complete (TLC), the
solvent was removed under reduced pressure, and the product was puri®ed by column

1060
B. P. Bandgar et al.: Mild Cleavage of Oximes
1
chromatography. Products were characterized by IR and H NMR spectroscopy as well as by
comparison with authentic samples.
References
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therein
[
[
[
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(
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7
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Received January 19, 1998. Accepted (revised) February 13, 1998