Pyridazine derivatives. Part 27: A joint theoretical and experimental approach to the synthesis of 6-phenyl-4,5-disubstituted-3(2H)-pyridazinones

A theoretical study of the structures of a series of 5-substituted-6-phenyl-3(2H)-pyridazinones has been carried out using quantum-mechanical calculations. This study indicates a significant effect of the nature of the substituent at the 5-position on the reactivity of this system. The results have also been confirmed by means of 1H NMR measurements. The outcome of this work has guided the development of novel and efficient synthetic pathways to obtain pharmacologically useful 6-phenyl-4,5-substituted-3(2H)-pyridazinones.