Two Reaction Modes of Pyridinium 1,4-Zwitterionic Thiolates with Sulfenes: Synthesis of 3H-1,2-Dithiole 2,2-Dioxides, 1,9a-Dihydropyrido[2,1-c][1,4]thiazines, and Indolizines.

Two reaction modes of pyridinium 1,4-zwitterionic thiolates with sulfenes generated in situ from alkanesulfonyl chlorides are described with DIPEA as the base. 3H-1,2-Dithiole 2,2-dioxides could be obtained via a formal [3 + 2] pathway from alkylmethanesulfonyl chlorides, while 1,9a-dihydropyrido[2,1-c][1,4]thiazines were obtained via a stepwise [(5 + 2) - 1] pathway from phenylmethanesulfonyl chlorides. Moreover, as an application, indolizines could be accessed via a stepwise {[(5 + 2) - 1] - 1} pathway, with 1,9a-dihydropyrido[2,1-c][1,4]thiazines as the transient intermediates.