1H, 13C and 15N NMR studies demonstrated that 9‐hydrazono‐6,7,8,9‐tetrahydro‐4‐oxo‐4H‐pyrido‐[1,2‐a] pyrimidlnes 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 by solvation and steric interaction.
ASJC Scopus subject areas
- Materials Science(all)