Mannich Reaction with Enaminones: Convenient Synthesis of Functionalized Tetrahydro-pyrimidines, Dihydro-1,3-oxazines, and Dihydro-1,2,4-triazepines

A series of tetrahydropyrimidines and bis-(tetrahydropyrimidines) was synthesized by Mannich reaction of sec-emaminones with formaldehyde and the appropriate amine or diamine. Whereas the reaction with formaldehyde gave the dihydro-1,3-oxazine. Tetrahydropyrimidines incorporating a phenolic Mannich base were obtained by Mannich reaction of the appropriate tetrahydropyrimidine. The bis(sec-enaminones) were used as precursors in synthesis of bis(tetrahydropyrimidines) and bis(dihydro-1,3-oxazines). Treatment of the appropriate sec-emaminone or bis(sec-enaminone) with hydrazine hydrate or phenylhydrazine and a suitable aldehyde afforded dihydro-1,2,4-triazepines and the bis(dihydro-1,2,4-triazepines).