Aluminium chloride: A mild and efficient catalyst for selective deprotection of 1,1-diacetates

Article abstract of DOI:10.1039/a807187j

A mild, efficient and excellent yield method for the selective deprotection of 1,1-diacetates to the corresponding aldehydes in the presence of aluminium chloride (AlCl₃) is described.

Full text of DOI:10.1039/a807187j

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272 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 272^273y
Aluminium Chloride: A Mild and Efficient Catalyst
for Selective Deprotection of 1,1-Diacetatesy
Iraj Mohammadpoor-Baltork* and Hamid Aliyan
Department of Chemistry, Esfahan University, Esfahan 81744, Iran
A mild, efficient and excellent yield method for the selective deprotection of 1,1-diacetates to the corresponding
aldehydes in the presence of aluminium chloride (AlCl3) is described.
Table 1 Deprotection of 1,1-diacetates in the presence of AlCl3
in refluxing MeCN
Selective introduction and removal of protecting groups is of
great signi¢cance in the total synthesis of complex organic
molecules. 1,1-Diacetates are synthetically useful and have
Time
Yield
(%)b
(t/min) Producta
received considerable attention, since these compounds are
Entry Substrate
10
moderately stable,1 easily prepared1
and can be used as
1
2
3
4
5
6
7
PhCH(OAc)2
15
7
5
5
5
PhCHO
2-MeOC6H4CHO 97
4-MeOC6H4CHO 99
4-ClC6H4CHO
4-BrC6H4CHO
4-MeC6H4CHO
2,5-(MeO)2-
98
protecting groups for the selective protection of aldehydes.
They are also important building blocks for the synthesis
of dienes for Diels^Alder cycloaddition reactions.11
Regeneration of the original aldehydes from their corre-
sponding 1,1-diacetates is a useful transformation in organic
2-MeOC6H4CHꢀOAc†
2
2
4-MeOC6H4CHꢀOAc†
4-ClC6H4CHꢀOAc†
93
97
99
99
2
4-BrC6H4CHꢀOAc†
4-MeC6H4CHꢀOAc2†
5
3
2
2,5-(MeO)2-
chemistry. Several methods for this purpose have been intro-
C6H3CHꢀOAc†
C6H3CHO
21
duced in the chemical literature.1;12
However, some of
2
8
9
10
11
12
13
2-O2NC6H4CHꢀOAc†
15
20
20
10
5
2-O2NC6H4CHO
3-O2NC6H4CHO
4-O2NC6H4CHO
PhCHˆCHCHO
5-Methylfurfural
98
98
95
98
99
2
the reported methods su¡er from drawbacks such as the
use of strong proton acids,12;13 long reaction time,1 low yield
of the product14 and the requirement for microwave
radiation.6;20;21
We now report a selective deprotection of 1,1-diacetates
under the catalysis of aluminium chloride in re£uxing
acetonitrile. As shown in Table 1, di¡erent 1,1-diacetates,
including those with electron-withdrawing substituents, are
converted into the corresponding aldehydes in excellent yields
(Scheme 1).
3-O2NC6H4CHꢀOAc†
4-O2NC6H4CHꢀOAc†
PhCHˆCHCHꢀOAc†
2
2
2
5-Me-2-furyl-CH(OAc)2
1-Naphthyl-CH(OAc)2
5
1-Naphthaldehyde 97
14
15
97
CH(OAc)2
CHO
OAc
O2N
OAc
O2N
15
10
88
AlCl3 CH3CN
RCHꢀOAc†
! RCHO
CH(OAc)2
OAc
CHO
OAc
2
reflux
Scheme 1
aAll products were identified by comparison of their physical and
spectral data with those of authentic samples. bIsolated yield.
It is noteworthy that deprotection of aryl aldehyde diacetates
occurs selectively without cleavage of phenolic acetate func-
tion (entries 14, 15). We have also tried the reaction of
1,1-diacetoxyheptane as an example of an aliphatic aldehyde
diacetate in re£uxing acetonitrile for 1h in the presence
of the catalyst. Only a 7% conversion into heptanal was
observed under these conditions. To stress the selectivity
of this method, we have performed a competitive reaction
Table 2 Reaction of phenylmethanediol diacetate to benzal-
dehyde with 0.4 molar equivalent of various Lewis acids in
refluxing MeCN
Entry
Metal halide
Yield(%)
between
4-methylphenylmethanediol
diacetate
and
1
2
3
4
5
6
7
ZnCl2
NiCl2
CeCl3
ZrCl4
CuCl2 Á 2H2O
MnCl2 Á 4H2O
CoCl2 Á 6H2O
69
60
10
9
79
48
65
1,1-diacetoxyheptane in the presence of a 0.4 molar ratio
of aluminium chloride and observed the following conver-
sions (Scheme 2).
AlCl3 CH3CN
4-MeC6H4CHꢀOAc† ‡ C6H13CHꢀOAc†
!
2
2
reflux; 15 min
4-MeC6H4CHO ‡ C6H13CHO
98% 2%
The catalytic e¡ects of several other Lewis acids for this
transformation were also studied. To this end, various metal
Scheme 2
Therefore, the present procedure o¡ers
deprotection of aryl aldehyde diacetates in the presence of
aliphatic aldehyde diacetate and phenolic acetate.
halides,
such
as
ZnCl2,
NiCl2,
CeCl3,
ZrCl4,
CuCl2 Á2H2O, MnCl2 Á4H2O and CoCl2 Á6H2O, were
reacted with phenylmethanediol diacetate in re£uxing
acetonitrile for 30 min. The experimental results show that
these Lewis acids are much less e¤cient for this purpose
(Table 2).
In conclusion, we have introduced an e¤cient method-
ology for the selective deprotection of aryl aldehyde
diacetates to the corresponding aldehydes.
a
selective
* To receive any correspondence.
y This is a Short Paper as de¢ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
therefore no corresponding material in J. Chem. Research (M).

View Article Online
J. CHEM. RESEARCH (S), 1999 273
6
7
8
9
P. Kumar, V. R. Hegde and T. P. Kumar, Tetrahedron Lett.,
1995, 36, 601.
Z.-H. Zhang, T.-S. Li and C.-G. Fu, J. Chem. Res. (S), 1997,
174.
T.-S. Jin, G.-Y. Du, Z.-H. Zhang and T.-S. Li, Synth. Com-
mun., 1997, 27, 2261.
B. P. Bandgar, N. P. Mahajan, D. P. Mulay, J. L. Thote and P.
P. Wadgaonkar, J. Chem. Res. (S), 1995, 470.
Experimental
Deprotection of 1,1-Diacetates.öGeneral Procedure. A solution of
1,1-diacetate (1mmol) in MeCN (5 ml) was treated with AlCl3
(0.4 mmol) and the mixture was stirred under re£ux conditions for
the time indicated in Table 1. The reaction was followed by GLC.
The solvent was evaporated and the resulting crude material was
puri¢ed on a silica-gel plate (eluent: CCl4 Et2O, 4 :1). Evaporation
of the solvent a¡orded the pure product; yield 88^99% (Table 1).
The reactions of nitro derivatives were performed in the presence of
a 0.5 molar equivalent of AlCl3.
10 N. Deka, D. J. Kalita, R. Borah and J. C. Sarma, J. Org.
Chem., 1997, 62, 1563.
11 B. B. Sinder and S. G. Amin, Synth. Commun., 1978, 8, 117.
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13 S. M. Tsang, E. H. Wood and J. R. Johnson, Org. Synth.,
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We are thankful to the Esfahan University Research Coun-
cil for partial support of this work.
14 C. Narayana, S. Padmanabhan and G. W. Kabalka,
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15 P. Cotelle and J.-P. Catteau, Tetrahedron Lett., 1992, 33, 3855.
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Received, 15th September 1998; Accepted, 4th January 1999
Paper E/8/07187J
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