METHYL AND PHENYLMETHYL NO)-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 no)-1-(methoxycarbonyl)ethenyl]amino}prop-2-enoate (4) and phen ylmethyl no)-1-(methoxycarbonyl)ethenyl]amino)prop-2-enoate (5) were p repared in three steps from the corresponding acetoacetic esters, and used as reagents for the preparation of N-3-protected 3-amino-4H-pyrid o[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. Fre e 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 me thods.