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

A new type of ortho-(alkynyl)benzyl thiosulfonates and ortho-(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 ortho-alkynyl benzyl thiosulfonates has been successfully achieved, producing sulfonyl-derived isothiochromenes as a major product through a favored 6-endo-dig 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.