Access to the 2,3‐dihydropyridazin‐3‐one and as‐triazino[3,4‐a]phthalazine ring systems from 4‐aryl‐2‐oxo‐butanoic acids

A novel series of 2,3‐dihydropyridazin‐3‐ones 15 were synthesized via condensation between hydrazines and 4‐( p ‐chlorophenyl)‐2‐hydroxy‐2‐(2‐oxo‐2‐substituted ethyl)butanoic acids 8 which in turn were prepared by the reaction of substituted benzylpyruvic acids 6 with methyl alkyl(aryl) ketones 7. Dehydration of 8b‐d by a mixture of glacial acetic acid and hydrochloric acid afforded 4‐( p ‐chorophenyl)‐2‐(substituted phenacyl)‐2‐butenoic acids 10. Condensation reaction of 10 with hydrazines gave type 15 compounds in good yields. Also, a new series of as ‐triazino[3,4‐ a ]phthalazines 20 was obtained from the reaction of substituted benzylpyruvic acids 6 with hydralazine to give the hydralazones 19 which underwent dehydrative cyclization reaction with PPA to afford 20. Structure assignments are based on 1 H, 13 C nmr and ir spectra.