Conjugate Reduction of α,β-Unsaturated Carbonyl Compounds Promoted by Nickel Nanoparticles

Abstract

The system composed of nickel(II) chloride, lithium metal, a catalytic polymer-supported arene, and ethanol, has been efficiently applied to the conjugate reduction of a variety of α,β-unsaturated carbonyl compounds (ketones and carboxylic acid derivatives) under very mild reaction conditions.

Key words

conjugate reduction - ketones - carboxylic acid derivatives - nickel - nanoparticles

References and Notes

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  We thank the referee for suggesting us to stress the nickel boride methodology.

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14

Alonso, F.; Osante, I.; Yus, M. submitted for publication.

17

The products 1,3-diphenylpropane-1-one, diisobutylketone, 3,3,5-trimethylcyclohexanone, (+)-dihydrocarvone, (-)-menthone, (+)-isomenthone, ethyl butyrate, ethyl hydro-cinnamate, ethyl succinate, and hydrocinnamic acid, were characterised by comparison of their chromatographic and spectral data with those of the corresponding commercially available pure samples. Dihydro-α-ionone, [19] dihydro-β-ionone, [20] , dihydroverbenone, [21] (+)-isodihydrocarvone, [22]
p-menthan-2-one, [22] , and hydrocinnamamide, [23] were characterised by comparison of their chromatographic and spectral data with those described in the literature.

18

General Procedure for the Conjugate Reduction of α,β-Unsaturated Carbonyl Compounds: Anhyd NiCl₂ (130 mg, 1 mmol) was added to a suspension of Li powder (29.4 mg, 4.2 mmol) and the vinylbiphenyl-divinylbenzene copolymer (52 mg, 0.05 mmol) in THF (2 mL) under an Ar atmosphere. After 10 min, a black suspension was formed indicating the generation of the nickel(0) nanoparticles. The suspension was diluted with THF (18 mL) followed by the addition of EtOH (0.13 mL, 2.2 mmol) and the substrate (1 mmol). The reaction course was monitored by GC-MS until the complete disappearance of the starting material. The resulting mixture was filtered through a pad containing celite (upper layer) and silica gel (lower layer) in a 3:1 ratio, dried over anhyd Na₂SO₄, and the solvent was evaporated under vacuum (15 Torr). Most of the reaction crudes did not need any further purification, whereas in some cases purification by column chromatography was applied (see footnotes in Table [1] ).