Allenyl Thianthrenium Salt: A Bench-Stable C Synthon for Annulation and Cross-Coupling Reactions.

Herein, we report the first bench-stable and nonhygroscopic monosubstituted allenyl sulfonium salt (ATT) synthesized from thianthrene and propargyl alcohol. We demonstrate its use in annulation chemistry to synthesize heterocycles, such as 2-hydroxy morpholine, 2-methyl quinoxalines, and benzodioxepinone derivatives, with an exocyclic double bond. The reagent is the first allenyl sulfonium salt that can undergo palladium-catalyzed cross-coupling reactions to form a C(sp)-C(sp) bond via Suzuki coupling and a C(sp)-C(sp) bond formation via reductive coupling.