A study on chemical behaviors of some 4-pyrones synthesized by one-step reactions towards various amines

Cycloaddition of acetylbenzoyl ketene generated in situ as an intermediate during one-step reaction between excess benzoylacetone and oxalylchloride to C=C double bond of cyclic enol form of benzoylacetone gave 3-acetyl-5-benzoyl-6-methyl-2-phenyl-4(4H)-pyrone 1a. Condensation reactions of 1a together with 3,5-dibenzoyl-2,6-diphenyl-4(4H)-pyrone 1b and 3-benzoyl-5-ethoxycarbonyl-2,6-diphenyl-4(4H)-pyrone 1c with two-fold excess primary amines provided a series of 3-benzoyl-1-alkyl-5-(1-alkylimino-ethyl)-6-phenyl-2-methyl-4(1H)-pyridinone 2, 3,5-dibenzoyl-1-alkyl-2,6-diphenyl-4(1H)-pyridinone 3a-c and 3-benzoyl-1-alkyl-5-ethoxycarbonyl-2,6-diphenyl-4(1H)-pyridinone 3d,e derivatives, respectively. In addition, while prolonged reaction of n-pentylamine with unsymmetrical pyrone derivative 1a gives a symmetrical pyridinone derivative namely 3,5-dibenzoyl-2,6-dimethyl-1-pentyl-4(1H)-pyridinone 5, much prolonged action n-pentylamine and then aqueous n-pentylamine on 1b resulted in degradation of the 4-pyrone ring to give dibenzoylmethane.