SHORT PAPER
1739
Microwave-Promoted Selective Regeneration of Carbonyl Compounds from
Oximes Using N-Bromosaccharin
S
elective Regenera
r
tion of
C
d
arbonyl Com
e
pounds fr
s
om
O
xime
h
s
ir Khazaei,* Abbas Amini Manesh
Department of Chemistry, Faculty of Sciences, Bu-Ali Sina University, P. O. Box 65178-4111, Hamadan, Iran
E-mail: a_khazaei@basu.ac.ir
Received 23 February 2004; revised 31 March 2004
Dissolution of oximes in acetone with addition of a small
Abstract: N-bromosaccharin was found to be an efficient reagent
for the oxidative cleavage of oximes to the corresponding aldehydes
and ketones under microwave irradiation in a domestic microwave
oven.
amount of water and subsequent reaction with NBSa un-
der microwave irradiation gave the corresponding carbo-
nyl compounds in good yields (Scheme 1).
Keywords: aldoxime, ketoxime, microwave, N-bromosaccharin
The results of the conversions of various oximes to their
corresponding carbonyl compounds are presented in
Table 1.
Oximes are very useful for protecting carbonyl groups in
organic synthesis.1 Oximes can be prepared from carbonyl
and non-carbonyl compounds.2 Deoximation of such
oximes provides an alternative method for the synthesis of
carbonyl compounds. Deprotection of an oxime can be
achieved by oxidative cleavage, reductive cleavage or by
hydrolytic cleavage, depending on the structural details of
the compound concerned. A number of oxidative deoxi-
mation methods have been developed which involve chro-
Even the sterically hindered ketone oxime (entry 13) was
successfully oxidatively cleaved to the corresponding ke-
tone in good yield. The aldoximes were converted to the
corresponding aldehydes and no acid was formed due to
over-oxidation of the regenerated aldehyde (entries 3, 4, 7
and 10). This procedure is also useful for the chemoselec-
tive oxidative deoximation of oximes in the presence of
alcohols or for oximes that contain -OH functional group
(entry 12). Thus, when equimolar mixtures of 2-chlo-
robenzaldoxime and benzyl alcohol in acetone and water
were allowed to react with NBSa under microwave irradi-
ation, the aldoxime underwent chemoselectively oxida-
tive deoximation giving benzaldehyde (90% yield),
whereas the benzyl alcohol were recovered unchanged
(Scheme 2).
mium(VI)
species
like
trimethyl
ammonium
chlorochromate,3 chlorotrimethylsilane-(chromium),4 py-
ridinium chlorochromate,5 pyridinium chlorochromate–
H2O2,6 trimethylsilyl chlorochromate,7 bis(trimethylsilyl)
chromate,8 supported and unsupported chromium triox-
11
ide,9,10 and polymer supported CrO3 as an oxidant. In
spite of the many available reagents, there is still a scope
for newer reagents as the existing oxidative methods suf-
fer from one or the other disadvantages like long reaction
times,12 difficulties in isolation of products,6 and forma-
tion of over-oxidation products leading to low yields.
On the other hand, after the reaction was completed N-
bromosaccharin (1) converted to saccharin (2). So it can
be isolated, brominated and reused as a new deoximating
reagent.
In conclusion, the striking features of our method are:
very short reaction times, formation of no over-oxidation
products due to high chemoselectivity and mild nature of
N-bromosaccharin, easy work-up procedure, high yields,
-OH functional group in the oxime structure does not ox-
idize to the carbonyl functional group, and finally, the ox-
idative reagent (NBSa) can be recovered and reused many
times.
Advantages such as cleaner reactions, very short reaction
times, and ease in work-up have kindled a special interest
in microwave chemistry.13 Therefore, we now report a
new oxidative method for deoximation under microwave
irradiation using N-bromosaccharin (NBSa), as an effec-
tive oxidising agent, that overcomes the disadvantages as-
sociated with oxidative methods developed so far.
Scheme 1
SYNTHESIS 2004, No. 11, pp 1739–1740
x
x.
x
x
.
2
0
0
4
Advanced online publication: 22.07.2004
DOI: 10.1055/s-2004-829163; Art ID: Z03604SS
© Georg Thieme Verlag Stuttgart · New York