Studies on isocyanides and related compounds; a facile synthesis of functionalized 3(2H)-pyridazinones via Ugi four-component condensation

The reaction between diarylglyoxal monohydrazones 1, isocyanides 2, aldehydes 3a-c, and methylene active acids 4 afforded a series of 3(2H)-pyridazinones 5 in a very simple manner. The intermediate Ugi four-component condensation products were never observed because of their tendency to cyclize. When the less reactive cyclopentanone (3d) is used instead of aldehydes 3a-c, satisfactory yields of 3(2H)-pyridazinones 7 were obtained by employing the pre-formed azine 8.