VSO4.5H2O: A mild and efficient catalyst for chemo-selective conversion of aldehydes to 1,1-diacetates

Article abstract of DOI:10.1002/jccs.200700040

Protection of aliphatic and aromatic aldehydes as 1,1-diacetates using VSO₄.5H₂O under solvent-free conditions is carried out. The products are obtained in good to excellent yields. Ketones are not affected under these conditions.

Full text of DOI:10.1002/jccs.200700040

Journal of the Chinese Chemical Society, 2007, 54, 273-275
273
Communication
VSO .5H O: A Mild and Efficient Catalyst for Chemo-selective Conversion
4
2
of Aldehydes to 1,1-Diacetates
Majid M. Heravi,* Khadijeh Bakhtiari, Tina Benmorad and Hossein A. Oskooie
Department of Chemistry, School of Sciences, Azzahra University, Vanak, Tehran, Iran
4 2
Protection of aliphatic and aromatic aldehydes as 1,1-diacetates using VSO .5H O under solvent-free
conditions is carried out. The products are obtained in good to excellent yields. Ketones are not affected
under these conditions.
Keywords: Vanadyl sulphate; 1,1-Diacetates; Aldehydes; Protection, Chemo-selective.
1
,1-Diacetates are useful as aldehyde protecting
1
yields in the presence of a catalytic amount of vanadyl sul-
fate at room temperature. (Scheme I, Table 1).
groups, as alternatives to acetals. Geminal or 1,1-diace-
tates are one of the most frequently used protecting groups
for aldehydes employed during multi-step organic synthe-
Scheme I
2
sis, because of their stability towards aqueous acids and
3
mild bases. Moreover, they can be used as building blocks
for the synthesis of dienes for Diels-Alder cycloaddition re-
4
actions. Also some industrial uses of these compounds,
which have been applied as cross-linking reagents for cel-
5
lulose in cotton and activators in the composition of
6
bleaching mixtures for wine-stained fabrics, have been re-
The aromatic aldehydes readily reacted with acetic
anhydride were shown to be better than aliphatic aldehydes
in the same reaction conditions. Furthermore longer reac-
tion times were required for a,b-unsaturated aldehydes in
order to obtain moderate yields of products. (Table 1, entriy
8).
ported.
Numerous methods are available in the literature for
the conversion of an aldehyde to the corresponding 1,1-di-
7
-16
acetate with acetic anhydride.
Solvent-free reactions
We found that aromatic ketones (entries 12, 13) were
practically unchanged in the reaction even after 24 h at ele-
vated temperature. Aromatic aldehydes bearing a variety of
functional groups namely electron-donating and electron-
have attracted the attention of chemists due to their envi-
ronmental and economical advantages and due to their
1
7
simplicity in process and handling. There is a need for a
greener catalytically efficient method, which might work
under mild and economically more inexpensive condi-
2
withdrawing groups reacted successfully with Ac O. These
reactions lead to completion in 30-90 min at room tempera-
ture to produce the corresponding diacetates in very high
yields (Table 1). To our surprise, the reaction did not pro-
ceed with furfuraldehyde.
1
8
4
tions. Recently, we have reported the use of KHSO ,
1
9
20
and 12-molibdophosphoric acid for the
CuSO
4
.5H
2
O
synthesis of 1,1-diacetates under solvent-free conditions.
To the best of our knowledge vanadyl sulphate has not been
used in organic synthesis. We now report that vanadyl sul-
fate, which is readily available, could be used as an effi-
cient catalyst for preparation of 1,1-diacetates from alde-
hydes because of its mild Lewis acidity. Various types of
aromatic and aliphatic aldehydes were cleanly and rapidly
converted to their corresponding 1,1-diacetates in excellent
We have also studied the competitive gem-diacyla-
tion reaction between benzaldehyde and benzophenone.
The former was chemo-selectively diacylated while benzo-
phenone did not yield any 1,1-diacetate in the presence of
4 2
VSO .5H O (Scheme II). Aldehydes having higher ground
state and lower activation energy compared to ketones hav-
ing lower ground state and higher activation energy are
*
Corresponding author. E-mail: mmh1331@yahoo.com

2
74 J. Chin. Chem. Soc., Vol. 54, No. 2, 2007
Heravi et al.
Table 1. Synthesis of 1,1-diacetates using VSO .5H O
4
2
m.p. (°C)
Reported
a
Entry
Substrate
benzaldehyde
Time (min)
Yield (%)
Found
2
2
2
2
2
2
1
2
3
4
5
4
1
2
3
4
5
6
7
8
9
30
35
99
85
94
80
99
99
99
70
44
81
44-45
4-methyl-benzaldehyde
2-methoxy-benzaldehyde
4-methoxy-benzaldehyde
4-chloro-benzaldehyde
3-nitro-benzaldehyde
4-nitro-benzaldehyde
cinamaldehyde
81-82
70-71
64-65
81-82
64-66
90
70
90
64-65
81
60
45
65-66
125
86
2
4
60
125-126
3
84-86
210
24 h
55
furfuraldehyde
No reaction
60
-
-
-
-
-
-
b
1
1
1
1
0
1
2
3
propionaldehyde
-
b
isobutyraldehyde
60
86
-
acetophenone
24 h
24 h
No reaction
No reaction
-
-
benzophenone
a
Yields refer to GC analysis.
Oily products were obtained.
b
Scheme II
more reactive than ketones. Therefore it is not surprising to
observe the chemo-selective diacylation of aldehydes over
ketones.
characterized by physical and spectra data.
General Procedure
In conclusion, a very simple and convenient catalytic
method has been developed for the synthesis of 1,1-diace-
tates from a variety of aldehydes under solvent-free condi-
tions. The method has advantages in terms of high yields,
high selectivity, short reaction times, ease of operation, and
use of relatively non-toxic, readily available and inexpen-
sive catalyst. We believe this protocol will be a useful addi-
tion to the modern synthetic methodologies.
To a mixture of aldehyde (1 mmol) and acetic anhy-
dride (3 mmol) mechanically stirred without solvent and at
room temperature the VSO
was added. After completion of the reaction as indicated by
TLC or GC, the catalyst was filtered and washed with Et
5 mL). Then the filtrate was washed with 5% NaHCO
mL) and brine (2 ´ 5 mL) successively and dried over MgSO
4 2
.5H O (20 mol%) as catalyst
2
O
(
3
(5
4
.
The solvent was evaporated under reduced pressure. The
crude product was purified over silica gel by column chro-
matography to provide the pure product in excellent yields.
EXPERIMENTAL
ACKNOWLEDGMENTS
Melting points were measured by using the capillary
1
tube method with an electro thermal 9100 apparatus. H
The authors are thankful to Azzahra University Coun-
cil for the partial financial support.
NMR spectra were recorded on a Bruker DRX-90 AVANCE
3
by using TMS as an internal standard (CDCl solution). IR
spectra were recorded as KBr disk on the FT-IR Bruker
Tensor 27. All products are known compounds, which were
Received July 18, 2006.

Chemo-selective Conversion of Aldehydes to 1,1-Diacetates
J. Chin. Chem. Soc., Vol. 54, No. 2, 2007 275
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