Formation of enamine Schiff bases by ring cleavage of pyridine

On treatment with diphenyldichloromethane or anisal chloride in the presence of acetone and aqueous sodium hydroxide, pyridine undergoes condensation and ring cleavage to yield the enamine Schiff bases 1,1-diphenyl-2-azadeca-1,3Z,5Z,7E-tetraen-9-one (1) and 1-(4-methoxyphenyl)-2-azadeca-1E,3Z,5Z,7E-tetraen-9-one (7). The reaction proceeds through attack of acetonyl carbanion on the initially formed bis-pyridinium salt, followed by ring scission with elimination of one equivalent of pyridine. The structure and stereochemistry of the 2-azatetraene (1) was confirmed by X-ray crystallography.