Reaction of 2-substituted-4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carbaldehyde oximes with electron-deficient olefins and acetylenes

A facile oxime–nitrone isomerization through the 1,2-hydrogen shift in 4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carbaldehyde oximes is discussed. The resultant NH-nitrones are trapped by maleimides to afford intermolecular cycloadducts. The reaction of the oximes with electron-deficient acetylenes undergoes via another path initiated by a nucleophilic attack of the oxime to acetylene moiety.