Enaminones as building blocks in organic syntheses: on the reaction of 3-dimethylamino-2-propenones with malononitrile

An X-ray crystal structure for the product of reacting enaminones and malononitrile in ethanol with piperidine conclusively established its structure as dienamides 4a,b that cyclize to 1,2dihydropyridine-3-carbonitriles 5 on treatment with acetic anhydride in the presence of hydrochloric acid. Reaction of 4a with a second mol equivalent of malononitrile afforded 2-[3-(dimethylamino)-3-phenyl-2-propenylidene]malononitrile 7 that was also converted into 5, and to 5-phenyl-1H-pyrazole 9 via treatment with hydrazine hydrate. Reaction of enaminone 1a with ethyl cyanoacetate in the presence of piperidine afforded the pyranone derivative 12.