New, simple and versatile synthesis of 4,6-disubstituted pyridazin-3(2H)-ones

A simple, two-step synthesis of 4,6-disubstituted pyridazin-3(2H)-ones starting from 2-diethoxyphosphoryl-4-oxoalkanoates and hydrazines is described. The intermediate 4-diethoxyphosphoryl-4,5-dihydropyridazin-3(2H)-ones obtained in this way are used in a Horner-Wadsworth-Emmons olefination of aldehydes to give a variety of disubstituted pyridazin-3(2H)-ones.