Synthesis of Aza-Michael, Michael, and 4-Heteryl-3(2H)-Pyridazinones from 4-(4-Bromophenyl)-4-Oxo-But-2-Enoic Acid

The 4-(4-bromophenyl)-4-oxo-buta-2-enoic acid (1) was reacted with nitrogen and carbon nucleophiles producing the aza Michael and Michael adducts depending on the reaction medium (neutral, acidic or alkaline). Hydrazinolysis of the aza Michael adducts obtained has afforded the 4-heteryl-3(2H)-pyridazinone derivatives 11a-c. The behavior of the latter compounds towards different nucleophilic and electrophilic reagents was investigated.