β-unsaturated ketones and aldehydes under the catalysis of silica gel. The 1,4-selectivity is satisfactorily high even in the reductions of polyenes conjugated to a carbonyl group. Methyl substituent at an olefinic position (α or β to the carbonyl group) retards the reduction. The reduction can be used as a useful tool in obtaining building blocks for the syntheses of terpenoids and their derivatives.