9
4 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
Synthesis of 1,1-Diacetates from Aldehydes using
1998, 94±95�
Trimethylchlorosilane and Sodium Iodide as Catalyst{
Nabajyoti Deka, Ruli Borah, Dipok J. Kalita and Jadab C. Sarma*
Regional Research Laboratory, Natural Products Chemistry Group, Organic Chemistry Division, Jorhat,
785006, Assam, India
A variety of aldehydes react with acetic anhydride in the presence of trimethylchlorosilane and sodium iodide or trimethylchloro-
silane alone to afford 1,1-diacetates in excellent yields.
Aldehydes may be protected as their 1,1-diacetates by a var-
iety of methods. These diacetates are synthetically useful as
for the preparation of 1,1-diacetates from aldehydes using
TMCS±NaI as catalyst.
When an aldehyde was treated with acetic anhydride
1
protecting groups having stability towards aqueous acids as
2
well as mild bases, and are useful as important building
blocks for the synthesis of dienes for Diels±Alder cyclo-
3 3
(1 ml of dry CHCl or CH CN was added to solubilise, if
needed) at room temp. [at 0±5 8C in case of hydroxycitronel-
lal (1)] in the presence of a catalytic amount of TMCS
(20 mol%) and sodium iodide (20 mol%) it yielded the cor-
responding diacetate in excellent yield (Table 1). The same
reaction took longer to complete in TMCS alone (reaction
in re¯uxing acetonitrile giving a comparable result). A blank
reaction of aldehyde, acetic anhydride and sodium iodide
failed to react even after 8 h of stirring at room temp.
Because of its high yield and short reaction time at ambient
3
addition reactions. Diacetates of some aldehydes are
reported to be good cross-linking reagents for cellulose in
4
cotton. One European patent claims the peroxygen com-
pounds of the type 1,1,5-triacetoxypent-4-ene as activators
in the composition of a bleaching mixture for wine stained
5
fabrics. Kula has successfully demonstrated in his patent
6
the utility of this protecting group in the synthesis of an
intermediate for chrysenthemic acid.
7,11
temperature this method will better many existing ones.
The catalyst is also easily available, cheap and easy to
handle.
Recently, several reports have appeared on the synthesis of
7
diacetates from aldehydes using dierent catalysts. Some
other methods employed for the preparation of 1,1-diace-
Experimental
8
tates from aldehydes include the use of protic acids, Lewis
Mps were determined on a Buchi capillary apparatus. IR spectra
were recorded on a Perkin Elmer 237B IR spectrophotometer.
NMR spectra were recorded on a Varian 360L instrument. Mass
spectra were recorded on a INCOS 50 GC-MS instrument.
General Procedure.ÐIn a typical reaction a mixture of 2 mmol of
benzaldehyde was treated at room temp. with 4 mmol of acetic
anhydride followed by 0.4 mmol of TMCS and 0.4 mmol of NaI.
9
, PCl
10
2
acids such as BF
3
3
,
Na®on-H. But in most cases, either a long reaction time
3
FeCl , etc. and the super acid
11
10
(
3
up to 120 h in the case of 2-furaldehyde with PCl ), or a
low product yield (4% in the case of 4-nitrobenzaldehyde )
is incurred. Herein we wish to report a high yielding method
10
a
Ta bl e 1
Reaction
time (t/min)
Yield
(%)
Mp (8C)
found/reported
Entry
Substrate
2
1
2
3
4
5
6
7
8
9
Benzaldehyde
25
40
40
50
60
40
30
50
87
92
96
96
70
84
70
90
45^46 (44^45 )
7
4-Cl-C
6
H
4
CHO
CHO
CHO
79^80 (79^80 )
7
4-NO -C
4-MeO-C
Furfural
2
6
H
4
125 (125 )
10
6
H
4
67^68 (67^68 )
7
55 (52^54 )
1
2
Butyraldehyde
2
Cinnamaldehyde12
85^86 (84^86 )
Crotonaldehyde
b
Gluteraldehyde
2
1
1
0
2
Acrolein
50
60
60
70 (2 + 3)
c
Hydroxycitronellal
a
All the compounds give satisfactory spectral analysis for IR, NMR (60 MHz) and MS. Yields are of isolated
b
c
pure products and mps are uncorrected. No reaction in 25% water solution. This reaction was carried
out at 0^5 8C in 60 min. The major products isolated were triacetate (2) (50% yield) and diacetate (3) (20%
yield) along with a complex mixture of minor products.
�To receive any correspondence.
�This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).
Deka, Nabajyoti
