β-Enaminoesters as building blocks in heterocyclic synthesis. A novel synthesis of fused azines by using blaise reaction as a key step

Ethyl bromoacetate 4 reacts with nitriles in the presence of activated zinc dust to afford the β-enaminoesters 7 and 19 . Compounds 7 and 19 show high reactivity towards a variety of reagents to give polyfunctional heterocyclic compounds. For example, the enaminoesters 7 and 19 react with benzaldehyde to give the 1,4 dihydropyridine derivatives 9 and 20 respectively. Isothiocyanates 24 (R = Ph, OEt) added to 19 to furnish pyrimidine-thiones 26 and 27 respectively. Structures and conceivable mechanisms are discussed