SiBr4/wet silica gel as an efficient heterogeneous system for cleavage of C=N

Article abstract of DOI:10.1016/j.tetlet.2003.09.208

A new and efficient method for the cleavage of oximes, hydrazones and semicarbazones has been achieved with SiBr₄/wet silica gel.

Full text of DOI:10.1016/j.tetlet.2003.09.208

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 9055–9056
SiBr /wet silica gel as an efficient heterogeneous system for
4
cleavage of CꢀN
Surya Kanta De
Department of Chemistry, University of Washington, Seattle, WA 98195, USA
Received 27 August 2003; revised 24 September 2003; accepted 25 September 2003
Abstract—A new and efficient method for the cleavage of oximes, hydrazones and semicarbazones has been achieved with
SiBr /wet silica gel.
4
©
2003 Elsevier Ltd. All rights reserved.
Oximes, hydrazones and semicarbazones are useful
protecting groups and are extensively used for purifica-
toxic or not readily available reagents, they need to be
freshly prepared and tedious work-up procedure.
Recently, some microwave irradiation techniques have
1
tion and characterization of carbonyl compounds.
2
6,7
Their synthesis from non-carbonyl compounds pro-
been developed which are valuable from the synthetic
vides an alternative pathway to aldehydes and ketones.
There has been considerable interest in the development
of mild techniques for the conversion of oximes into
their corresponding carbonyl compounds. Although
some of the known methods are carried out under mild
reaction conditions, most of them require drastic condi-
tions, high temperature, long reaction times, expensive,
standpoint but extreme precaution have to be taken as
these reactions were perfomed under microwave irradi-
ation or ultrasonic irradiation with an oxidant. Most of
the known methods deal for the regeneration of car-
bonyl compounds from oximes only, a little attention
has been paid for the regeneration of carbonyl com-
3
–5
8
–10
pounds from hydrazones and semicarbazones.
Table 1. Deprotection of oximes, hydrazones and semicarbazones with SiBr /wet silica gel at room temperature
4
Entry
Substrate
Time (min)
Product
Yielda (%)
1
2
3
4
5
6
7
8
9
4-Chloroacetophenone semicarbazone
Benzophenone semicarbazones
Acetophenone semicarbazone
4-Methoxyacetophenone semicarbazone
Benzaldehyde semicarbazone
3-Nitrobenzaldehyde semicarbazone
4-Bromobenzaldehyde semicarbazone
Cyclohexanone semicarbazone
4-Methoxybenzaldehyde semicarbazone
Benzophenone phenylhydrazone
4-Chloroacetophenone phenylhydrazone
4-Bromobenzaldehyde phenylhydrazone
2-Nitrobenzaldehyde phenylhydrazone
Cyclohexanone oxime
10
18
24
14
17
22
15
14
18
26
15
19
28
16
220
280
68
35
4-Chloroacetophenone
Benzophenone
Acetophenone
4-Methoxyacetophenone
Benzaldehyde
3-Nitrobenzaldehyde
4-Bromobenzaldehyde
Cyclohexanone
4-Methoxybenzaldehyde
Benzophenone
4-Chloroacetophenone
4-Bromobenzaldehyde
2-Nitrobenzaldehyde
Cyclohexanone
93
91
86
89
83
87
89
90
88
87
91
90
79
85
10
11
12
13
14
15
16
17
18
b
Acetophenone oxime
Benzophenone oxime
Benzaldehyde oxime
4-Bromobenzaldehyde oxime
Acetophenone
Benzophenone
Benzaldehyde
4-Bromobenzaldehyde
83
89
90
87
b
a
Yields refer to pure isolated products, characterized by IR, 1H NMR and MS.
Under reflux condition.
b
0
040-4039/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2003.09.208

9
056
S. K. De / Tetrahedron Letters 44 (2003) 9055–9056
In this paper I wish to report a convenient and efficient
method for the regeneration of carbonyl compounds
from semicarbazones, hydrazones and oximes using
concentrated. The residue was chromatographed on
silica gel, (eluted hexane–ethyl acetate: 8/2) to afford
4-chloroacetophenone in 93% yield and there was no
evidence for the formation of any side products. Similar
treatment of oximes and hydrazones gave the corre-
sponding carbonyl compounds in 79–91% yield as sum-
marized in the Table 1.
SiBr in the presence of wet silica gel.
4
Table 1 summarizes the results of the conversions of
various oximes, hydrazones and semicarbazones to
their corresponding carbonyl compounds. Semicarba-
zones and hydazones were deprotected very rapidly at
room temperature into their corresponding carbonyl
compounds. It should be noted that above mentioned
reactions did not proceed using wet silica gel alone,
SiBr alone, SiBr with ordinary silica gel alone even
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4
4
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4
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11
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tetrachloride (125 mL) was stirred at room temperature
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completion of the reaction, the mixture was filtered and
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4