Reduction of 1 : 4-Diketones

Abstract

THE dibenzoylethylenes on reduction with metal combinations or catalytic hydrogenation under certain conditions yield the corresponding diphenacyls¹, and there is evidence that the reaction occurs through 1 : 6-addition of hydrogen followed by rapid ketonization of the intermediate dienols¹. Lutz and Reveley² showed the presence of one such dienol, without, however, isolating it : Confirmation of this mechanism is desirable, especially since 1 : 6-addition is comparatively uncommon³. We have done this by reducing several substituted dibenzoylethylenes with aluminium isopropoxide in isopropyl alcohol, a reagent known to attack carbonyl groups while leaving olefinic linkages intact. The reduction products were invariably the corresponding diphenacyls, identified (after chromatographic adsorption) by mixed melting points with authentic samples. Since direct hydrogenation of the carbon - carbon double bonds is ruled out, the reduction must have taken the course outlined above.