Transformation of 1,5-Diphenylpentane-1,3,5-trione. The Synthesis of Substituted (4H)-Pyranones, Pyridin-4(1H)-ones and 4H-Pyrano[3,2-c]pyridin-4-ones

Abstract

1,5-Diphenylpentane-1,3,5-trione (1) was transformed by the reaction either with N,N-dimethylformamide dimethyl acetal (DMFDMA) or N,N-dimethylacetamide dimethyl acetal (DMADMA) into (N,N-dimethylamino)methylidene derivatives 2a,b as intermediates.They were converted in the presence of silica gel into 5-benzoyl-2-phenylpyran-4-one (3a) and its 6-methyl derivative 3b, while the corresponding 5-benzoyl-2-phenylpyridin-4(1H)-one (4) was formed by the reaction with NH 4 Cl.Compound 3b gave the corresponding (N,N-dimethylamino)methylidene derivative 5 with DMFDMA, which was cyclized in aqueous ammonia into 2,5-diphenyl-4H-pyrano[3,2-c]pyridin-4-one (7).The reaction of 1 with excess of DMFDMA followed by reaction with ammonia or primary amines yielded 1-substituted 3,5-dibenzoylpyridin-4(1H)ones (9a-m).