Chemistry Letters Vol.32, No.4 (2003)
367
acidic reaction medium. A few acid sensitive aldehydes such as
piperonal (entry 5), furfural (entry 10) and thiophene aldehyde
(entry 11) are also diacetylated by this procedure without any
difficulty. Most significantly, the conversion under the catalysis
of Zn(BF4)2 are relatively fast (1.5–4 h) compared to the
procedure using more expensive LiBF4 (16–25 h).5g
In a similar procedure, when the aldehyde was stirred with a
mixture of acetic anhydride and potassium cyanide in methylene
chloride in the presence of an aqueous solution of Zn(BF4)2
(0.6 mol%) at room temperature for 3–20 h the corresponding
cyanoacetate was obtained in good yield. The results are
presented in Table 2. It has been observed that for an efficient
reaction a large excess (10–13 equiv.) of KCN is required9 and
without any solvent the reaction became exothermic and
vigorous. Methylene chloride has been found to be the solvent
of choice. In general, all the reactions are very clean and high
yielding. However, it has been observed that ketones remained
inert under the present procedure, making it selective for
aldehydes.
molecules, e) truly catalytic, and f) cost efficiency. We believe,
this will offera better and more practical alternative tothe existing
procedures.4{6 Further expansion of the use of this catalyst for
other useful reactions are in progress.
This work has enjoyed the financial support from CSIR, New
Delhi [Grant No. 01(1739)/02]. J. D. and A. D. are also thankful
to CSIR for their fellowships.
References
1
2
3
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4
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yields, d) mild reaction condition compatible with sensitive
5
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Table 2. The Zn(BF4)2 catalyzed conversion of aldehydes to
1,1-cyanoacetates
OAc
CN
Zn(BF4)2
+ Ac2O
+
RCH
RCHO
KCN
CH2Cl2, rt
Entry Aldehyde
Time/h Yield/%a
1
2
3
4
5
6
7
8
PhCHO
4-(Cl)-C6H4CHO
Piperonal
4-(OMe)-C6H4CHO
Furfural
Thiophene-2-carboxaldehyde
3-(O-allyl)-C6H4CHO
Cinnamaldehyde
C9H19CHO
Crotonaldehyde
Citral
5
5
8
9
5
20
8
3
6
3
98
98
92
83
87
78
90
80
63
62
54
6
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L. F. Fieser and M. Fieser, ‘‘Reagents for Organic Synthesis,’’
John Wiley & Sons, Inc., New York, Vols. 1–17.
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1985 (1999). b) B. C. Ranu, S. Samanta, and S. Guchhait,
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7
8
9
10
11
3
9
Y. N. Belokon, A. V. Gutnov, M. A. Mosakalenko, L. V.
Yashkina, D. E. Lesovoy, N. S. Ikonnikov, V. S. Larichev, and
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aYields refer to pure isolated products characterized by
spectral data (IR, 1H, 13C NMR).