been found that reduction of CdC bond depends significantly
on the electron deficiency of alkene, and thus, relatively less
electron-deficient CdC bonds in R,R-dicarboalkoxy alkenes
and R-cyano, R-carboalkoxy olefins did not undergo reduc-
tion at all. On the other hand, substitution on the aromatic
ring of the â-aryl moiety also greatly influences the reduction.
Thus, m-methoxy phenyl enone (entry 14) underwent smooth
reduction, whereas the corresponding o-and p-methoxy
phenyl analogues failed to go for such reduction.
In general, the reductions by this procedure are clean, high-
yielding, and reasonably fast. The reaction conditions are
mild enough to tolerate acid-sensitive functionalities such
as methoxy (entries 10,14), methylenedioxy (entry 11), and
carboxylic ester (entries 19 and 20). This reagent is also
highly chemoselective, reducing only the electron-deficient
CdC bond without affecting several easily reducible func-
2
tional groups such as -CtN, -CdO, and -CO R.
To conclude, the present procedure using indium metal
in aqueous ethanolic ammonium chloride provides a chemo-
selective reduction of the CdC bond in highly activated
alkenes. The notable advantages of this procedure are as
follows: (a) operational simplicity, (b) exclusive compat-
ibility with several acid-sensitive and easily reducible func-
tionalities, (c) good yields, and (d) green chemistry. More-
over, this study constitutes a systematic investigation of the
reduction of a CdC bond with scopes and limitations by
indium metal, and certainly it broadens the perview of further
research in this area.
(
6) General Experimental Procedure. 1,1-Dicyano-2-phenyl ethylene
(
entry 5) (154 mg, 1 mmol) was heated under reflux at an oil bath
temperature of 90 °C with indium (173 mg, 1.5 mmol) (commercially
available ingot from SRL, India, cut into small pieces) in aqueous ethanolic
ammonium chloride solution (1.5 mL of EtOH, 1.5 mL of H2O, 1 g of
NH4Cl) for 9 h (TLC). Ethanol was removed under vacuum, and the residue
was extracted with ether. The extract was washed with brine, dried (Na2-
SO4), and evaporated to leave the crude product, which was purified by
column chromatography over silica gel (eluting solvent system, hexanes-
ether in 98:2 ratio) to furnish the corresponding alkane (135 mg, 86%) as
-
1 1
a white solid, mp 87 °C: IR 2255 cm ; H NMR (300 MHz, CDCl3) δ
1
3
3
.29 (2H, d, J ) 6.9 Hz), 3.91 (1H, t, J ) 6.9 Hz), 7.26-7.47 (5H, m); C
NMR (75 MHz, CDCl3) δ 25.0, 36.8, 112.1(2), 128.8, 129.1(2), 129.3(2),
32.9. Anal. Calcd for C10H8N2: C, 76.90; H, 5.16. Found: C, 76.59; H,
.05. This procedure has been followed for the reduction of all conjugated
1
5
Acknowledgment. This investigation has enjoyed finan-
cial support from the CSIR, New Delhi. J.D is thankful to
CSIR for his fellowship.
alkenes listed in Table 1. The compounds have been characterized by their
1
13
physical and spectral (IR, H NMR and C NMR) data in comparison with
the reported values whenever available and by elemental analysis.
(7) Dickens, F.; Horton, L.; Thorpe, J. F. J. Chem. Soc. 1924, 1830;
Chem. Abstr. 1925, 19, 268.
Supporting Information Available: Spectral and ana-
lytical data for all reduced products (alkanes), not reported
earlier, designated by their entries in Table 1.
(
(
(
8) Russel, P. B.; Hitchings, G. H. J. Am. Chem. Soc. 1952, 74, 3443.
9) Goodrich, B. F. Chem. Abstr. 1959, 53, 1258f.
10) Davies, R. E.; Haworth, R. D.; Jones, B.; Lamberton, A. H. J. Chem.
Soc. 1947, 191.
(
(
11) Hughes, E. C.; Johnson, J. R. J. Am. Chem. Soc. 1931, 53, 737.
12) Weizmann, Ch.; Bergmann, E.; Haskelberg, L. Chem. Ind. 1937,
OL016296A
5
87.
(13) Fytas, G.; Foscolos, G. B.; Vyzas, A.; Garoufalias, S. Chem. Abstr.
(14) Schwall, H.; Sobotta, R. Chem. Abstr. 1991, 115, 90685x (European
1
991, 115, 8442j.
Patent).
Org. Lett., Vol. 3, No. 16, 2001
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