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‐4 H ‐pyrido‐[1,2‐ a ]pyrimidin‐4‐ones

Methyl 2‐acetyl‐3‐{[2‐(dimethylamino)‐1‐(methoxycarbonyl)ethenyl]amino}prop‐2‐enoate ( 4 ) and phenyl‐methyl 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 , 5 H ‐thiazolo[3,2‐ a ]pyrimidin‐5‐one 13 , 4 H ‐pyrido[1,2‐ a ]‐pyridin‐4‐one 19 and 2 H ‐1‐benzopyran‐2‐ones 20 – 23 . Free 3‐amino‐4 H ‐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‐[(phenyl‐methoxy)carbonyl]but‐1‐envl as N ‐protecting group by various methods.