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, 1H and 13C 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 σm and σ− constants of the substituents present on the phenyl ring.
ASJC Scopus subject areas
- Organic Chemistry