The synthesis of 1,4-diketones

Abstract

Recent methods for the synthesis of 1,4-diketones are briefly reviewed.Zinc and phenacyl bromide in dimethoxyethane afforded 1,4-diphenylbutane-l,4-dione in moderate yield, but other solvents or metals examined gave no or a lower yield. The route is unsatisfactoryfor aliphatic 1,4-diketones. Attempts to use 'levulinyl chloride' to acylate olefins or acetylenes were fruitless. Routes involving aldol condensations of hexane-2,5-dione or its monoacetal had very restricted success, as did those depending on the halogenolysis of acyl derivatives of phenacylmalonic ester. A fairly general route to 1,4-diketones was found in the sequence: valine to N-acylvaline to oxazol-5-one to Michael addition product with an α, β-unsaturated ketone followed by alkaline hydrolysis.The Michael addition is not regiospecific and valine derivatives may also be isolated. Yields of 1,4-diketones are only moderate but the synthesis is quick and convenient.