Trimethylsilyl Triflate‐Promoted Synthesis of Enone Functionalized Benzo‐1,3‐Thiazines via Formal [4 + 2] Heteroannulation of Azadienes with β‐Ketodithioesters at Room Temperature

An efficient approach for the direct synthesis of previously inaccessible enone functionalized benzo‐1,3‐thiazines has been developed via formal [4 + 2] heteroannulation of azadienes (generated in situ from 2‐aminobenzyl alcohol) with β‐ketodithioesters in acetonitrile at room temperature, facilitated by trimethylsilyl triflate (TMSOTf). This strategy is distinguished by transition‐metal and additive‐free mild conditions, convenient operation, wide functional group compatibility with no steric and electronic constraints, accessible scalability, high yields, and practical transformations. A combination of controlled experiments and HRMS studies corroborated the proposed mechanism.