Clay supported bis-(trimethylsilyl)-chromate: An efficient reagent for oxidative deoximation

Article abstract of DOI:10.1007/s007060070045

A convenient method for the direct conversion of oximes to carbonyl compounds upon treatment with clay supported BTSC under classical heating as well as microwave irradiation in a solvent-free system is described.

Full text of DOI:10.1007/s007060070045

Monatshefte f uÈ r Chemie 131, 1109±1113 (2000)
Clay Supported Bis-(trimethylsilyl)-chromate:
An Ef®cient Reagent for Oxidative Deoximation
Majid M. Heravi1 , Dariush Ajami , Mahmood Tajbakhsh ,
and Mitra Ghassemzadeh
;Ã
2
3
2
1
Department of Chemistry, School of Sciences, Azzahra University, Tehran, Iran
2
Chemistry and Chemical Engineering Research Center of Iran, Tehran, Iran
3
Department of Chemistry, University of Mazandaran, Badolsar, Iran
Summary. A convenient method for the direct conversion of oximes to carbonyl compounds upon
treatment with clay supported BTSC under classical heating as well as microwave irradiation in a
solvent-free system is described.
Keywords. Oxidative deoximation; Clay supported BTSC; Microwave irradiation.
Introduction
Selective protection and deprotection of functional groups is of great importance in
synthetic organic chemistry. In the last decade oximes have received much
attention, being not only used to purify and isolate carbonyl compounds, but also to
protect and activate carbonyl groups [1]. Since oximes can also be prepared from
noncarbonyl compounds [2], an ef®cient method of deoximation can be considered
as an alternative pathway to aldehydes and ketones.
The hydrolytic stability of oximes has inspired the development of several
reagents, e.g. trimethylammonium chlorochromate [3], dinitrogen tetroxide [4],
pyridinium chlorochromate [5], chromium trioxide-chlorotrimethylsilane [6], clay
supported ferric nitrate [7], titanium silicate [8], tert-butylhydroperoxide [9], N-
haloamides [10], manganese triacetate [11], activated MnO2 [12], sodium
periodate-silica [13], bismut trichloride [14] ammonium persulfate-silica gel
[15], Dess-Martin periodinane [16], and tetrabutylammonium peroxydisulfate [17].
Each of the above reagents has its own merits and drawbacks.
Reagents deposited on mineral supports have gained popularity in organic
synthesis due to their selectivity and ease of manipulation [18]. Montmorillonite
clays have been extensively used as ef®cient supports for a variety of organic
reagents [18]. Recently we have used supported bis-(trimethylsilyl)-chromate
(
BTSC) as an ef®cient and versatile reagent in organic synthesis [19]. In
continuation of our program devoted to the development of surface active catalysts
20] along with environmentally benign synthetic protocols utilizing microwave
[
à Corresponding author

1110
M. M. Heravi et al.
irradiation under solvent-free conditions [21], we report a facile and high-yield
deoximation procedure catalyzed by clay supported bis-(trimethylsilyl)-chromate
at room temperature and under microwave irradiation in a solventless system.
Results and Discussion
In a typical reaction, 1±1.2 equivalents of BTSC supported on montmorillonite K10
were added to a stirred solution of oxime in dry CH Cl (Scheme 1). The mixture
2
2
was stirred at room temperature until the reaction was complete; then it was ®ltered
and washed with dichloromethane. Evaporation of the solvent gave the
Table 1. Oxidative cleavage of oximes with clay supported BTSC in CH Cl
2
2
a
c
Substrate
Carbonyl
Reaction time
min
Yield
%
b
compound
a
b
All substrates were synthesized by known literature procedures; all products were characterized
1
by comparison of their m.p. as well as their IR and H NMR spectra with those of authentic samples;
c
yields refer to isolated products

Deoximation with Bis-(trimethylsilyl)-chromate
1111
Scheme 1
corresponding carbonyl compounds. Several examples illustrating this method are
summarized in Table 1.
In connection with our interest in using microwaves to increase the reaction
rates [21], the above deoximation was performed under microwave irradiation in a
solventless system by mixing 1±1.2 equivalents of BTSC-clay with 1 equivalent of
an oxime in a beaker and irradiating for 2 min. It is noteworthy to mention that in
the absence of clay in both cases the reactions were seriously sluggish and,
a
Table 2. Solid state deoximation using BTSC-clay under microwave irradiation
Substrate
Carbonyl
Reaction time
(min)
Yield
(%)
compound
a
For comments, cf. footnotes to Table 1

1112
M. M. Heravi et al.
moreover, in the latter case molten BTSC adhered to the walls of the reaction
vessel, forming an intractable solid mass which made the isolation of carbonyl
compounds dif®cult and led to erratic results. To assess the generality of this solid
state deoximation, a variety of oximes were reacted under these conditions
affording the corresponding carbonyl compounds in high yield and very short
reaction times (Table 2).
In conclusion, BTSC supported onto montmorillonite K10 is a simple and
inexpensive reagent for the oxidative deoximation of oximes at room temperature
both in solution and under solvent-free conditions using a household microwave
oven. Solvent-free microwave irradiation is advantageous over conventional
heating, offering a practical and environmentally benign protocol, decreasing
reaction times and, in some cases, giving cleaner reactions and easier work-up.
Experimental
All products are known compounds and identi®ed by comparision with authentic samples. BTSC
supported on clay was prepared according to the procedure of Ref. [19b].
General procedure for the oxidative cleavage of oximes
3
To a solution of 10 mmol oxime in 20 cm CH Cl , 8 g BTSC supported on montmorillonite K10
2
2
(
corresponds to 11 mmol CrO ) were added. The reaction mixture was stirred at room temperature
3
for 10 min. The progress of the reaction was monitored by TLC (eluent: light petrol ether:ethyl
3
acetate ˆ 8:2). The mixture was ®ltered, and the solid material was washed with 20 cm CH Cl . The
2
2
®ltrate was evaporated to dryness, and the crude material was puri®ed on a silica gel pad to afford the
corresponding carbonyl compound (Table 1).
Deoximation of oximes with BTSC supported on clay under microwave irradiation
in a solventless system
BTSC supported on 1.7 g montmorillonite K10 (corresponding to 2.2 mmol of CrO ) and 2 mmol
3
oxime were crushed together in a mortar to form an intimate mixture. The mixture was transferred to
a beaker and placed under microwave irradiation for the time indicated. The progress of the reaction
was monitored by TLC. After completion of the reaction, the residue was taken up with CH Cl ,
2
2
3
®
ltered, washed with 10 cm CH Cl , and the ®ltrate was evaporated to dryness. Final puri®cation
2 2
was achieved by passing the residue through a silica gel pad (Table 2).
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Deoximation with Bis-(trimethylsilyl)-chromate
1113
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Received March 20, 2000. Accepted (revised) May 19, 2000
È
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