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.