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Reduction of Nitroolefins with Raney Nickel and Sodium Hypophosphite

A mild method for converting nitroolefins into ketones (or aldehydes)

Tetrahedron Letters, Vol. 24, No.4, pp 417-418, (1983)

Summary:

Nitroolefins are converted into the corresponding saturated ketones or aldehydes in high yield by treatment with Raney nickel and sodium hypophosphite in aqueous ethanol at pH 5.

Nitroolefins are of great synthetic potential in organic chemistry and several ways are known to convert them into carbonyl or amino derivatives1-4. However, current methods for reducing vinyl nitro compounds to saturated ketones or aldehydes2 either require reagents which are incompatible with acid-ensitive and reducible functional groups within the molecule1d, 3, 4 or proceed by a two-step process4.

We wish to report here a chemoselective method for effecting the direct conversion of nitroalkenes into ketones or aldehydes in high yield under mild conditions. This method involves the treatment of the nitroolefin with sodium hypophosphite and Raney nickel in ethanolic solution at pH 5 (see Table) . Ester groups, C=C bonds, nitro and halogen substituents on aromatic nuclei, carbonyl groups are not affected by this reducing system5.

General Experimental Procedure:

A suspension of Raney nickel (2.5 ml) and an aqueous solution of sodium hypophosphite (14 g in 60 ml) were added (in several portions and under stirring) to a solution of the nitroolefin (14 mmol) in ethanol-aqueous acetate buffer, pH 5 (2:1, ca. 400 ml). After 2 hr at 40-60°C the catalyst was filtered off, water added and the solution extracted with ether. Evaporation of the solvent yielded the carbonyl compound that could bepurified by either distillation or crystallization.

Table 1
Nitroolefins Carbonyl compounds Isolated
yields
Ph-CH=C(CH3)NO2 Ph-CH2-CO-CH3
88%
p-MeO-Ph-CH=CC(CH3)NO2 p-MeO-Ph-CH2-CO-CH3
92%
p-Br-Ph-CH=CC(CH3)NO2 p-Br-Ph-CH2-CO-CH3
77%
o-OH-Ph-CH=CC(CH3)NO2 o-OH-Ph-CH2-CO-CH3
70%
p-OH-Ph-CH=CC(CH3)NO2 p-OH-Ph-CH2-CO-CH3
56%
Ph-CH=CH-CH=CC(CH3)NO2 Ph-CH2-CH=CH-CO-CH3
64%
 

It must be pointed out that under the conditions reported here nitroparaffins are reduced to amines whilst oximes give the corresponding carbonyl compounds in almost quantitative yields6. Thus the above procedure represents also a very mild method for deoximation which appears complementary to those in the literature1.

 

 

 

 

References

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