N-Methylpiperidinium chlorochromate adsorbed on alumina: A new deoximation reagent

Article abstract of DOI:10.1007/s007060170038

N-Methylpiperidinium chlorochromate adsorbed on alumina was found to be an efficient and selective reagent for the mild oxidative cleavage of oximes.

Full text of DOI:10.1007/s007060170038

Monatshefte f uÈ r Chemie 132, 1229±1231 (2001)
N-Methylpiperidinium Chlorochromate
Adsorbed on Alumina: A New Deoximation
Reagent
Mahmood Tajbakhsh1 , Majid M. Heravi , Farajollah Mohanazadeh1,
Siavosh Sarabi , and Mitra Ghassemzadeh
;Ã
2;Ã
2
3
1
Department of Chemistry, University of Mazandaran, Babolsar, Iran
2
3
Department of Chemistry, School of Sciences, Azzahra University, Vanak, Tehran, Iran
Chemistry and Chemical Engineering Research Center of Iran, Tehran, Iran
Summary. N-Methylpiperidinium chlorochromate adsorbed on alumina was found to be an ef®cient
and selective reagent for the mild oxidative cleavage of oximes.
Keywords. N-Methylpiperidinium chlorochromate; Deoximation; Supported reagent; Carbonyl
compounds.
Introduction
Oximes are easily obtained from carbonyl compounds and have great potential as
intermediates in organic synthesis [1]. They are also useful protecting groups in
multistep organic syntheses [2] and have found extensive application in the isolation
and puri®cation of carbonyl compounds [3]. Their synthesis from non-carbonyl
compounds offers an alternative route to aldehydes and ketones [4, 5]. Oximes are
hydrolytically stable, and this advantage has inspired the development of several
reagents for their oxidative cleavage. In recent years reagents such as trimethyl-
ammonium chlorochromate [6], pyridinium chromate-hydrogen peroxide [5],
triethylammonium chlorochromate [7], chromic anhydride-chlorotrimethylsilane
[8], bismuth trichloride [9], sodium periodate supported on wet silica [10], activated
MnO [11], Ti HP [12], Des-Martin periodinane [13], and tetrabutyl ammonium
2
3
peroxydisulfate [14] have been reported. Reagents impregnated on mineral solid
supports [15, 16] have gained popularity in modern organic synthesis [17];
accordingly, deoximation reactions using solid supports have also been developed
[18, 19].
We have recently reported that N-methylpiperidinium chlorochromate adsorbed
on alumina is a selective reagent for the oxidation of benzylic alcohols to the
corresponding carbonyl compounds [20] as well as that deoximation reactions on
solid supports proceed under eco-friendly conditions [21±23]. Armed with these
à Corresponding authors. E-mail: mmheravi@azzahra.ac.ir

1230
M. Tajbakhsh et al.
experiences, a method for the cleavage of oximes under mild conditions seemed to
be at hand.
In this communication we report on N-methylpiperidinium chlorochromate
adsorbed on alumina as a new reagent for the cleavage of oximes under non-
aqueous conditions.
Results and Discussion
In a typical procedure, acetophenone oxime and N-methylpiperidinium chloro-
chromate supported on alumina were re¯uxed in dioxane. The progress of the
reaction was monitored by TLC using CHCl :CCl ˆ 3:1 as eluent. Filtration,
3
4
removal of the solvent, and puri®cation of the residue by column chromatography
on silica gel afforded acetophenone in almost quantitative yield. Using the reagent
without mineral support results in a sluggish reaction, and considerable amounts of
starting material are present even after prolonged reaction times. Among various
supports (silica gel, montmorillonite K-10, zeolite), alumina was found to give the
best results.
To assess the generality of the method, a variety of oximes were treated with this
reagent under the same conditions to afford the corresponding carbonyl compound
in high to excellent yields (Table 1).
In conclusion, the described procedure has advantages over previously reported
methods and provides a facile, useful, and important addition to the existing
methodologies. The notable advantages are mild reaction conditions, easy work-up,
excellent yields, and minimization of side products.
Table 1. Deoximation with N-methylpiperidinium chlorochromate adsorbed on alumina
a
Reaction time
min
Yield
0
Substrate
R
R
Product
%
1
1
1
1
1
1
1
1
a
b
c
d
e
f
H
Ph
2a
2b
2c
2d
2e
2f
30
60
40
40
60
60
80
85
92
90
92
90
92
90
82
71
H
4-Cl-Ph
2-Cl-Ph
4-Me-Ph
Ph
H
H
Me
Me
Ph
Ph
4-OMe-Ph
Ph
g
h
2g
2h
4-Cl-Ph
a
Yields refer to isolated and puri®ed products
Experimental
Yields refer to pure isolated products. All compounds are known and were characterized by com-
parison of their physical and spectroscopic data with those of authentic samples. N-Methylpiperi-
dinium chlorochromate was synthesized according to a reported procedure [20].

Deoximation with N-Methylpiperidinium Chlorochromate
1231
Conversion of acetophenone oxime to acetophenone; typical procedure
3
In a round bottomed ¯ask (50 cm ) equipped with a condenser and magnetic stirrer, a mixture of
3
0.315 g acetophenone (1 mmol) in 10 cm dioxane was prepared. N-methylpiperidinium chlorochro-
mate supported on alumina (1 g, prepared by mixing 0.5 g of reagent and 0.5 g of alumina) was added
to this solution and re¯uxed for 60 min. Reaction progress was monitored by TLC (eluent:
CHCl3:CCl4 ˆ 3:1). After completion of the reaction the mixture was ®ltered, and the solid material
3
was washed with 10 cm dioxane. The ®ltrates were combined and evaporated. The resulting crude
material was further puri®ed on a silica gel column with an appropriate eluent to afford the
corresponding carbonyl compound (Table 1).
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Received March 1, 2001. Accepted March 22, 2001
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