NITROGEN BRIDGEHEAD COMPOUNDS .81. SYNTHESIS OF 9-(BENZYLIDENEHYDRAZONO)-6-METHYL-4-OXO-6,7,8,9-TETRAHYDRO-4H-PYRIDO[1,2-A-]PYRIMIDINE-3-CARBOXYLATES AND 9-(BENZYLIDENEHYDRAZINE)-6-METHYL-4-OXO-6,7-DIHYDRO-4H-PYRIDO[1,2-A]-PYRIMIDINE-3-CARBOXYLATES

Reaction of ethyl 9-hydrazono-6-methyl-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylate and benzaldehyde and its derivatives give a tautomeric mixture of 9-arylidenehydrazono-6,7,8,9-tetrahydro-and 9-arylidenehydrazine-6,7-dihydropyrido[1,2-a]pyrimidine derivatives. In the same case the enhydrazine and hydrazone tautomers were separated. The structure of the products were characterised by uv, ir, H-1 and C-13 nmr. The equilibrium of the tautomers was affected by the substituent of the phenyl ring. A fair linear correlation exists between the logarithms of the equilibrium constants and Hammett sigma(m) and sigma- constants of the substituents present on the phenyl ring.