Vicinal Thiosulfonylation of <i>ortho</i>-(Alkynyl)benzyl Thiosulfonates/Sulfurothioates for Direct Synthesis of Sulfonyl-Derived Isothiochromenes

A new type of <i>ortho</i>-(alkynyl)benzyl thiosulfonates and <i>ortho</i>-(alkynyl)benzyl sulfurothioates (Bunte salts) have been prepared for the first time to investigate vicinal thiosulfonylation. A unique Au-catalyzed atom transfer radical cyclization (ATRC) of <i>ortho</i>-alkynyl benzyl thiosulfonates has been successfully achieved, producing sulfonyl-derived isothiochromenes as a major product through a favored 6-<i>endo-dig</i> cyclization. Additionally, the vicinal thiosulfonylation of Bunte salts with sodium sulfinates has been realized under the influence of Mn(OAc)₃·2H₂O to afford 4-sulfonyl-isothiochromene derivatives exclusively. A range of sulfonyl-derived isothiochromenes were readily accessed in promising yields, including gram-scale reactions. Of note, postsynthetic transformations and possible mechanistic insights were uncovered.