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

This work utilizes in situ -generated ketenes as dienophiles in [4 + 2] cycloadditions with heterodienes, providing a novel strategy for the synthesis of both 4-alkyl-substituted and 4-unsubstituted pyridazin-3(2 H )-ones.