Methyl (Z)-2-[(Benzyloxycarbonyl)amino]-3-dimethyl- aminopropenoate in the Synthesis of Heterocyclic Systems. Synthesis of (Benzyloxycarbonyl)amino Substituted Fused Pyrimidinones

Methyl (Z)-2-[(benzyloxycarbonyl)amino]-3-dimethylaminopropenoate (1) was used as a reagent for preparation of 3-[(benzyloxycarbonyl)amino] substituted 4H-pyrido[1,2-a]pyrimidin-4-ones 17-21, 4H-pyrimido[1,2-b]pyridazin-4-ones 22 and 23, 5H-[1,2,4]triazolo[2,3-a]- pyrimidin-5-one 24, 5H-thiazolo[3,2-a]pyrimidin-5-one 25, and 4H-pyrazino[1,2-a]pyrimidin-4-one 26. Removal of the benzyloxycarbonyl group by catalytical transfer hydrogenation with Pd/C in the presence of cyclohexene is selective to give 3-amino-4H-pyrido[1,2-a]- pyrimidin-4-ones 27-30 in 85-92% yields, or with hydrogen bromide in acetic acid to give 3-amino-4H-pyrimido[1,2-b]pyridazin-4-one (31) and 6-amino-5H-thiazolo[3,2-a]pyrimidin-5-one (32) in 80% yields.