An efficient and selective method for conversion of oximes and semicarbazones to the corresponding carbonyl compounds under solvent-free conditions

Article abstract of DOI:10.1081/SCC-100104002

1-Benzyl-4-aza-1-azoniabicyclo[2.2.2]octane dichromate (BAABCD) is a useful reagent for selective conversion of oximes and semicarbazones to the corresponding carbonyl compounds. The reaction was carried out under solvent-free conditions and in the presence of a catalytic amount of aluminum chloride.

Full text of DOI:10.1081/SCC-100104002

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AN EFFICIENT AND SELECTIVE
METHOD FOR CONVERSION OF
OXIMES AND SEMICARBAZONES
TO THE CORRESPONDING
CARBONYL COMPOUNDS
UNDER SOLVENT-FREE
CONDITIONS
a
a
A. R. Hajipour , S. E. Mallakpour , I.
b
a
Mohammadpoor-Baltork & S. Khoee
a
Pharmaceutical Research Laboratory , College
of Chemistry, Isfahan University of Technology ,
Isfahan, I.R., 84156, Iran
b
Department of Chemistry , Isfahan University ,
Isfahan, I.R., 81744, Iran
Published online: 09 Nov 2006.
To cite this article: A. R. Hajipour , S. E. Mallakpour , I. Mohammadpoor-Baltork &
S. Khoee (2001) AN EFFICIENT AND SELECTIVE METHOD FOR CONVERSION OF OXIMES
AND SEMICARBAZONES TO THE CORRESPONDING CARBONYL COMPOUNDS UNDER
SOLVENT-FREE CONDITIONS, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 31:8, 1187-1194, DOI:
10.1081/SCC-100104002
To link to this article: http://dx.doi.org/10.1081/SCC-100104002

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SYNTHETIC COMMUNICATIONS, 31(8), 1187–1194 (2001)
AN EFFICIENT AND SELECTIVE
METHOD FOR CONVERSION OF OXIMES
AND SEMICARBAZONES TO THE
CORRESPONDING CARBONYL
COMPOUNDS UNDER SOLVENT-FREE
CONDITIONS
1
,
1
A. R. Hajipour, * S. E. Mallakpour,
2
I. Mohammadpoor-Baltork, and S. Khoee
1
1
Pharmaceutical Research Laboratory, College of
Chemistry, Isfahan University of Technology,
Isfahan, 84156, I.R. Iran
Department of Chemistry, Isfahan University,
Isfahan, 81744, I.R. Iran
2
ABSTRACT
1-Benzyl-4-aza-1-azoniabicyclo[2.2.2]octane dichromate
BAABCD) is a useful reagent for selective conversion of
(
oximes and semicarbazones to the corresponding carbonyl
compounds. The reaction was carried out under solvent-
free conditions and in the presence of a catalytic amount of
aluminum chloride.
Oximes and semicarbazones are highly crystalline and very useful
for the purification and characterization of carbonyl compounds. These
*
Corresponding author.
1
187
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

1
188
HAJIPOUR ET AL.
derivatives are also useful as efficient protecting groups for aldehydes and
1
ketones. Conversion of oximes back to their corresponding carbonyl com-
pounds is a very important process in synthetic organic chemistry. Several
oxidative deoximation methods have been developed that have some advan-
2
–16
tages over the classical hydrolysis method.
In recent years, little effort has been made to develop efficient and mild
methods for the oxidative cleavage of semicarbazones, and only a few
reports are available for the deprotection of these derivatives to the corre-
1
4–22
sponding carbonyl compounds.
Heterogeneous reactions that are facilitated by supported reagents on
2
3–25
various solid inorganic surfaces have received attention in recent years.
The advantage of these methods over conventional homogenous reactions is
that they provide greater selectivity, enhanced reaction rates, cleaner prod-
ucts, and manipulative simplicity. In continuation of our ongoing program
2
6–29
to develop environmentally benign methods using solid supports,
we report the synthesis of 1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane
dichromate. This reagent is readily prepared by reaction of an aqueous
solution of 1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (2) with
CrO in 3N NCl at room temperature, as shown in Scheme 1.
3
The resulting orange powder, which can be stored for months without
loss of activity, is soluble in acetonitrile, acetone, and N,N-dimethylforma-
Scheme 1.
mide, and slightly soluble in chloroform, ethylacetate, and dichloromethane,
but is not soluble in carbon tetrachloride, n-hexane, or diethylether.
1-Benzyl-4-aza-1-azoniabicyclo[2.2.2]octane dichromate (BAABCD)
3) is an efficient and novel reagent for the oxidative cleavage of the
(
C ¼ N bond of oximes and semicarbazones in the presence of aluminum
chloride. Using reagent (3) in the presence of 0.1 molar ratio of aluminum
chloride, various oximes and semicarbazones have been successfully depro-
tected to their corresponding aldehydes and ketones in good to excellent
yields. The process involves simply mixing BAABCD, aluminum chloride,
and oximes or semicarbazones in a mortar (Scheme 2) and grinding the
mixture for the time specified in Tables 1 and 2 at room temperature.

OXIME AND SEMICARBAZONE CONVERSION
1189
The yields of the reactions are excellent (79–95%) and the reaction times are
exceedingly short (20–55 s). Under these conditions, the reagent cannot con-
vert phenylhydrazones and 2,4-dinitrophenylhydrazones to the correspond-
ing carbonyl compounds.
1
The compounds (5a–5o) and (7a–7n) were characterized by H NMR
and IR analysis.
Scheme 2.
Notably, aldehydes did not undergo further oxidation to their car-
boxylic acids under the reaction conditions.
To evaluate the effect of aluminum chloride in this reaction, we tried
the reaction of acetophenone oxime with reagent (3) without using any
aluminum chloride. The reaction did not proceed at all after 30 min grinding
the reaction mixture. The mechanism of the reaction is the same as has been
reported by us for the oxidation of alcohols by this reagent (30).
Another noteworthy advantage of the reagent is the exclusive oxida-
tion of oximes, irrespective of the presence of semicarbazone. When a
mixture of an equimolar amount of 3,4-dimethoxybenzaldehyde oxime
(
4b) and 2,5-dimethoxy benzaldehyde semicarbazone (5 g) was treated
with reagent (3), only the oxime (4b) was selectively oxidized to the
corresponding carbonyl compound and the semicarbazone (5 g) remained
unchanged (Eq. 1).
Treatment of acetophenone oxime (4l) in the presence of 1-biphenyl
ethanol, led to exclusive oxidation of benzylic alcohol to the corresponding
ketone in 100% yield (Eq. 2).
Eq. 1

1
190
HAJIPOUR ET AL.
a
Table 1. Conversion of Oximes to Carbonyl Compounds
ꢀ
ꢀ
M.p.( C) or b.p.( C)/Torr
b
Yield (%)
33
Substrate
Time (s)
30
Found
Reported
4
a
b
89
184–186187
4
30
9641–43
42–45
4
4
c
40
35
91
88
49–51
49–50
50–52
49–51
d
4
4
e
f
25
40
85
93
121–122/10
230/760
113–116/6
232/760
4
4
g
h
45
52
9681–83
93
82–85
107–108
108–110
4
4
4
4
i
43
30
35
20
95
79
85
91
76–79
78–80
130–131/760
155/760
j
129–131/760
153–155/760
200/760
k
l
202/760
4
4
m
n
27
87
90
116–118
56–59
115–118
57–59
40
4
o
2692
124–127/10
0
248/76
a
1
Products were confirmed by comparison with authentic samples (IR, H-NMR,
b
TLC); Yield of isolated pure carbonyl compound.

OXIME AND SEMICARBAZONE CONVERSION
1191
a
Table 2. Conversion of Semicarbazones to Carbonyl Compounds
ꢀ
ꢀ
M.p.( C) or b.p.( C)/Torr
b
Time (s) Yield (%)
33
Substrate
Found
Reported
5
a
b
37
45
92
95
34–37
76–79
35–37
78–80
5
5
5
c
50
56
91
89
107–109
200/760
108–110
202/760
d
5
5
e
f
45
40
86121–122/10
/16 13–116
90
185–187
187
5
5
5
5
5
5
g
h
i
39
50
50
45
35
50
9644–47
45–48
56–59
91
87
93
90
92
57–59
50–52
49–52
53–55/10
48–50
j
162/760
49–51
k
l
35–38
36–39
5
5
a
m
n
55
35
87
90
213–215/760
124–127/10
213–214/760
248/760
1
Products were confirmed by comparison with authentic samples (IR, H-NMR,
b
TLC); Yield of isolated pure carbonyl compound.

1
192
HAJIPOUR ET AL.
Eq. 2
When we treated ꢀ,ꢁ-unsaturated oxime and its semicarbazone deri-
vative, only the C ¼ N bond was selectively oxidized to the corresponding
carbonyl compounds, and the reagent was ineffective in oxidizing C ¼ C
double bond (Tab. 1 and 2).
In conclusion, we have reported a new and efficient methodology for
the regeneration of aldehydes and ketones from oximes and semicarbazones
under solvent-free conditions. The stability and easy preparation of
BAABCD, easy work-up procedure, and high yields of the products,
make this method a novel and useful one relative to the reported method
for regeneration of carbonyl compounds from their derivatives. These
results make BAABCD a bench-top oxidizing agent.
EXPERIMENTAL
Products were characterized by comparison with authentic samples
1
IR, H-NMR spectrum, m.p. and b.p.). All m.p. were taken on a
(
Gallenkamp melting apparatus and are uncorrected. Elemental analyses
were performed by the Research Institute of Petroleum Industry,
1
Tehran, I. R. Iran. All H-NMR were recorded at 90 MHz in CDCl /
3
CCl4 relative to TMS (0.00 ppm), and IR spectra were recorded on a
Shimadzu 435 IR spectrophotometer. Spectra of solids were carried out
using KBr pellets.
Preparation of 1-Benzyl-4-aza-1-azoniabicyclo[2.2.2]octane
Dichromate 3
CrO (4.2 g, 0.042 mol) in 3 N HCl was added dropwise to a solution
3
3
1,32
of 1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (2).
.042 mol) in a minimal amount of water. Precipitated orange solid was
filtered off and then washed with water and dried under vacuum to yield
5.6g (98%) of 1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane dichromate (3).
(10 g,
0
2

OXIME AND SEMICARBAZONE CONVERSION
1193
ꢀ
ꢀ
1
M.p. 178 –180 C (dec). H NMR (CDCl , TMS): ꢂ 7.60 (s, 5H); 4.52 (s,
3
2
H); 3.6–2.9 (two overlapping triplets, 12H). Anal. calc. for C H Cr N O :
26 38 2 2 7
C, 52.52; H, 6.44; Cr, 17.49; N, 4.71%. Found: C, 52.40; H, 6.60; Cr, 17.40;
N, 4.60%.
Deprotection of Oximes (4a–4t) and Semicarbazones (6a–6n) with
Reagent (3) Under Solvent-Free Conditions: General Procedure
The deprotection of benzophenone oxime is representative for depro-
tection of oximes and semicarbazones. A mixture of benzophenone oxime
(
0.16g, 0.803 mmol), 1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane dichro-
mate (0.50 g, 0.803 mmol), and aluminum chloride (11 mg, 0.08 mmol) was
crushed with a mortar and pestle for 35 s until TLC showed complete dis-
appearance of starting oximes (Tab. 1). CCl (10 mL) was added to the
4
reaction mixture and, after vigorous stirring, the mixture was filtered off.
The solvent was evaporated by rotary evaporator to give pure benzophe-
none (0.129 g, 88%).
ACKNOWLEDGMENTS
We thank the Isfahan University of Technology Research Council
for the partial support of this work.
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Received April 24, 2000