TBAI/K2S2O8-Promoted [4 + 2] Annulation of Ketene N,S-Acetals and N-Tosylhydrazones toward Pyridazines.

A TBAI/K2S2O8-promoted [4 + 2] annulation of ketene N,S-acetals, and N-tosylhydrazones was efficiently developed, enabling straightforward access to a variety of trisubstituted pyridazines in reasonable to good yields. The synthetic methodology features a broad substrate scope and a good functional group tolerance. Control experiments demonstrated the indispensability of the alkylthio functionality in the enaminone substrates.