Ketenes as dienophiles in aza-Diels–Alder reactions with dicyanohydrazones for accessing pyridazin-3(2H)-ones

Abstract

This study introduces a novel [4 + 2] cycloaddition strategy for the synthesis of biologically significant 4-alkyl-substituted/unsubstituted pyridazin-3(2H)-ones. This approach utilizes tautomerized dicyanohydrazones as heterodienes and in situ-generated ketenes as dienophiles. Density functional theory (DFT) calculations revealed that the reaction follows an inverse-electron-demand (IED) [4 + 2] cycloaddition mechanism, driven by the interaction between the HOMO of the ketene and the LUMO of the tautomerized dicyanohydrazone.