Structural Studies on 9-Hydrazono-6,7,8,9-tetrahydro-4-oxo-4H-pyridopyrimidines by 1H, 13C and 15N NMR Spectroscopy

Article abstract of DOI:10.1002/omr.1270211111

1H, 13C and 15N NMR studies demonstrated that 9-hydrazono-6,7,8,9-tetrahydro-4-oxo-4H-pyrido-<1,2-a>pyrimidines exist as an equilibrium mixture of Z-E isomers in the hydrazono-imino tautomeric form having an exocyclic double bond.Proton-catalysed Z-E interconversion is fast.Substituent and solvent effects revealed that the decisive factors controlling the Z:E ratio are internal hydrogen bonding in the Z-isomer, stabilization and steric interaction.