Chemoselective preparation of oximes, semicarbazones, and tosylhydrazones without catalyst and solvent

Article abstract of DOI:10.1007/s007060170126

A simple and versatile method for the synthesis of oximes, semicarbazones, and tosylhydrazones of aldehydes in the presence of ketones without catalyst and solvent is presented.

Full text of DOI:10.1007/s007060170126

Monatshefte fuÈr Chemie 132, 403±406 (2001)
Chemoselective Preparation of Oximes,
Semicarbazones, and Tosylhydrazones
without Catalyst and Solvent
Ã
Lav S. Uppalla, and Rahul Govande
Babasaheb P. Bandgar , Vaibhav S. Sadavarte,
Organic Chemistry Research Laboratory, School of Chemical Sciences, Swami Ramanand Teerth
Marathwada University, Vishnupuri, Nanded-431 606, India
Summary. A simple and versatile method for the synthesis of oximes, semicarbazones, and
tosylhydrazones of aldehydes in the presence of ketones without catalyst and solvent is presented.
Keywords. Protection; Deprotection; Microwaves; Aldehydes; Ketones.
Introduction
The protection of carbonyl compound as oximes, semicarbazones, and tosylhydra-
zones is of great interest in synthetic organic chemistry [1]. In addition to their
protective function they allow for the isolation, puri®cation, and characterization of
aldehydes and ketones [1, 2]. Further, oximes of aldehydes and ketones may serve
as selective ꢀ-activating groups [3a] and intermediates for many reactions such as
the preparation of amides by Beckmann rearrangement [2]. The synthesis of oximes
from non-carbonyl compounds provides an alternative pathway to aldehydes and
ketones [3b].
The classical methods for the preparation of oximes, semicarbazones, and
tosylhydrazones involve the use of acids [4] or bases [5] as catalysts and thus are
subject to limitations if the carbonyl compounds contain acid or base labile
functional groups. The economic attractiveness of patented methods of oximation
[6, 7] is limited by the use of H2O2 and low yield [7]. An exhaustive survey of the
literature [8] reveals that there has been no report on the preparation of oximes,
semicarbazones, and tosylhydrazones without catalyst. We report here for the ®rst
time the selective preparation of these compounds from aldehydes in the presence of
ketones using microwaves without catalyst and solvent.
Ã
Corresponding author

404
B. P. Bandgar et al.
Results and Discussion
Oximes, semicarbazones, and tosylhydrazones of aldehydes (Scheme 1) were pre-
pared using hydroxylamine, semicarbazide, and tosylhydrazine under microwave
irradiation (Table 1). Except in the case of 2,4-dichlorobenzaldehyde and salicyl-
aldehyde, syn and anti oximes were formed which have different physical and
biological activities [9]. However, 2,4-dichlorobenzaldehyde and salicylaldehyde
gave only syn-2,4-dichloro and 2-hydroxybenzaldoximes. It is worth mentioning
that the aldehyde group was selectively protected in the presence of the ketone
group (Table 2) as con®rmed by IR spectroscopy. When the reaction of 4-chloro-
benzaldehyde and hydroxylamine was carried out at 100ꢀC for 4 h the corre-
sponding oxime was obtained in 50% yield, and the remaining starting material
could be recovered.
Scheme 1
Table 1. Synthesis of oximes, semicarbazones, and tosylhydrazones without catalyst and solvent using
microwave irradiation
Substrate
Producta
Reaction
time/min
Yieldb/%
Substrate
Producta
Reaction
time/min
Yieldb/%
1a
1b
1c
1d
1e
1f
2a
2b
2c
2d
2e
2f
0.80
0.66
1.25
0.75
4.00
0.75
0.50
0.80
92
92
97
88
87
94
88
85
1i
2i
0.25
0.25
0.25
0.25
0.25
0.20
0.25
0.20
92
92
90
89
92
89
92
89
1j
2j
1k
1l
2k
2l
1m
1n
1o
1p
2m
2n
2o
2p
1g
1h
2g
2h
a
Products were characterized by their physical constant, IR spectra, and by comparison with
b
authentic samples [5, 10] yields are of pure isolated products

Chemoselective Protection of Aldehydes
405
Table 2. Selective protection of aromatic aldehydes as oximes, semicarbazones, and tosylhydrazones
Substrate
Producta
Reaction
time/min
Yielda/%
1q
1r
1s
1.5
1.2
0.5
0.25
87
92
91
87
1t
a
Products were characterized by their physical constants, IR spectra, and by comparison with
authentic samples [5, 10]
Experimental
A Kelvinator T-37 oven (2450 MHz) was used for microwave irradiation. IR spectra (KBr pellets)
1
were recorded with a Bomem MB-104 FTIR spectrometer. H NMR spectra were measured with a
300 MHz (Bruker AC 300F) instrument; the chemical shifts are given relative to TMS as internal
standard. Solvents were distilled before use. All chemicals were of analytical grade. Reactions were
monitored by TLC.
General method for the preparation of oximes, semicarbazones, and tosylhydrazones
A paste of a mixture of aromatic aldehyde (5 mmol) and hydroxylamine (5 mmol), semicarbazide
(5 mmol), or tosylhydrazine (5 mmol) in methanol (few drops) was exposed to microwaves (heating
and cooling at intervals of 15 s and 1 min for the speci®ed time. After completion of the reaction
(TLC) the product was extracted with 3 Â 5 cm3 CH2Cl2. Removal of the solvent under reduced
pressure gave pure product in excellent yields.
Acknowledgements
V. S. Sadavarte thanks CSIR, New Delhi, for a Junior Research fellowship.

406
B. P. Bandgar et al.: Chemoselective Protection of Aldehydes
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Received June 28, 2000. Accepted (revised) August 25, 2000