1302
G. P. Romanelli et al. / Tetrahedron Letters 44 (2003) 1301–1303
As a part of an ongoing research project to develop
environmentally amicable organic reactions, we report
here a rapid preparation of 1,1-diacetates of aldehydes
using the WD acid, being tested as a homogeneous
catalyst. The protection reaction (Scheme 1) was stud-
ied using aldehydes 1a–1s as the substrates.† Their
structure and the obtained results are shown in Table 1.
Benzaldehyde (1a) was chosen for optimizing the reac-
tion conditions: temperature, time, concentration of the
solutions and molar ratio of the WD acid to substrate
were checked.
diacetate in 98% (2n). The nature of the substituent on
the aromatic ring seems to have no relevant effect on
the reaction, see e.g. entries 4, 8, 10 and 11; but
hydroxyaldehydes 1h, 1i and 1k gave the corresponding
triacetates. Aliphatic aldehydes were also protected
with very good yields (entries 17–19).
Some aliphatic and aromatic ketones were also checked
for the reaction: acetone, butanone, acetophenone and
ethyl n-butyl ketone, they have not reacted under the
described experimental conditions. Likewise, 4-
dimethylaminobenzaldehyde failed to give the expected
1,1-diacetate.
The selected experiments were carried out at 20°C in 1
M solutions and varying the reaction times and the
amount of catalyst used. When 1% (mmol) WD acid
was added, the higher yield of 1,1-diacetate 1a was
attained at 30 min reaction at room temperature,
shorter and longer times gave lower yields. Besides,
using 5% catalyst and keeping unchanged other reac-
tion conditions, yields were 1–5% higher than the ones
recorded in Table 1, and when a reduction to a half on
the amount of solvent was tried (other conditions as
described below in general procedure) yields fell by
2–4%. Both benzaldehydes (1a–1l) and naphthalde-
hydes (1n,1o) gave excellent yields of the corresponding
acylals. For example 4-nitrobenzaldehyde (1e) gave 4-
nitrophenylmetanediol diacetate (2e) in 92% and 1-
naphthaldehyde (1n) gave 1-naphthylmetanediol
All the products were characterized by comparison
(GLC, TLC and physical constants) with authentic
samples prepared by the conventional method,3b using
sulfuric acid as the catalyst. All the yields were calcu-
lated from crystallized products, their purity was estab-
lished by GLC, being better than 98%. The WD acid
(H6P2W18O62·24H2O) was prepared as described
elsewhere8 from an aqueous solution of a/b
K6P2W18O62·10H2O salt, which was treated with ether
and concentrated (37%) HCl solution.
Studies are in progress in our laboratory in relation to
the use of recoverable, supported catalysts.
General procedure for the protection of aldehydes
Table 1. Catalytic conversion of aldehydes in acylals using
A mixture of aldehyde 1 (1 mmol), acetic anhydride (1
mL) and WD catalyst (1% mmol, ca. 45 mg) was stirred
at room temperature for 30 min and then ethyl ether
(10 mL) was added to the reaction mixture. The result-
ing solution was successively washed with 1 M NaOH
and water, dried over anhydrous Na2SO4, and filtered.
The solution was then concentrated, and the solid crude
product was recrystallized from petroleum ether yield-
ing each of the pure acylals 2.‡
WD acid
Entry Aldehydes 1a–s
R
Acylals 2a–s yield
(%)a
1
2
3
4
5
6
7
8
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
Ph
2-ClC6H4
4-ClC6H4
95
93
93
92
92
93
97
94b
95b
96
92b
90
98
98
97
88
89
90
95
2-O2NC6H4
4-O2NC6H4
3-PhOC6H4
4-MeSC6H4
2-HOC6H4
3-HOC6H4
2-Cl-6-FC6H3
3-MeO-4-HOC6H3
2-Br-3,4-(OMe)2C6H2
PhCHꢀCH
1-C10H7
Conclusions
9
The above described procedure provides a useful alter-
native for the preparation of 1,1-diacetates from alde-
hydes, being general, rapid, selective and inexpensive,
and having a low environmental impact.
10
11
12
13
14
15
16
17
18
19
2-C10H7
2-Furyl
n-C3H7
n-C5H11
Acknowledgements
s
n-C9H19
Financial support from CONICET (Argentina), and
Universidad Nacional de La Plata is gratefully
acknowledged. H.J.T., G.P.R. and G.T.B. are members
of CONICET.
a Reactions were performed at 20°C and 30 min reaction time, using
1% (mmol) of WD acid. Yields are expressed from crystallized
products (see text).
b Compounds 2h, 2i and 2k are triacetates of 1h, 1i and 1k, respec-
tively.
‡ As an example, spectroscopic data for the novel compound 2l are
given: 1H NMR (CDCl3) l 7.87 s (1H), 7.04 s (1H), 7.03 s (1H),
3.91 s (3H), 3.88 s (3H), 2.14 (6H). 13C NMR (CDCl3) l 168.2,
150.6, 148.6, 126.8, 115.6, 113.0, 110.5, 89.4, 56.23, 56.16, 20.71.
† Starting aldehydes were commercial, they were initially purified to
match the reported physical data.
Romanelli, Gustavo P.
