Methyl and phenylmethyl 2-acetyl-3-{[2-(dimethylamino)-1-(methoxycarbonyl)ethenyl]amino}prop-2-enoate in the synthesis of heterocyclic systems:: Preparation of 3-amino-4H-pyrido-[1,2-a]pyrimidin-4-ones

Methyl 2-acetyl-3-([2-(dimethylamino)-1-(methoxycarbonyl)ethenyl]amino}prop-2-enoate (4) and phenylmethyl 2-acetyl-3-{[2-(dimethylamino)-1-(methoxycarbonyl)ethenyl]amino)prop-2-enoate (5) were prepared in three steps from the corresponding acetoacetic esters, and used as reagents for the preparation of N-3-protected 3-amino-4H-pyrido[1,2-a]pyrimidin-4-ones 10-12, 5H-thiazolo[3,2-a]pyrimidin-5-one 13, 4H-pyrido[1,2-a]pyridin-4-one 19 and sH-1-benzopyran-2-ones 20-23. Free 3-amino-4H-pyrido[1,2-a]pyrimidin-4-ones 24-26 were prepared from 10-12 by removal of the 2-(methoxycarbonyl)-3-oxobut-1-enyl or 3-oxo-2-[(phenylmethoxy)carbonyl]but-1-enyl as N-protecting group by various methods.