关键词: 可见光催化, 砜基化, 硫化, 硫代磺酸酯, 远程碳-氢键官能团化

Due to the prevalence of organosulfur compounds in pharmaceuticals, agrochemicals, and functional materials, the development of new efficient and practical methods for the construction of C—S bonds is highly desirable in organic synthesis. Recently, the radical sulfonylation of alkenes has attracted considerable attention because of its efficient and versatile synthesis of organosulfur compounds under mild reaction conditions. The previous methods usually involve the formation of one C—S bond. In contrast, the thiosulfonylation of alkenes represents a highly attractive protocol for the concurrent formation of two distinct C—S bonds. Herein, a novel visible-light photocatalytic remote thiolation of aldehydes triggered by the radical sulfonylation of unactivated alkenes has been developed, with readily available thiosulfonates as both the sulfonating and thiolating reagents, successfully giving 6- or 7-sulfonylated thioesters in moderate to high yields with broad substrate scope and excellent atom-economics. As compared to the traditional methods that are limited to 1,2- or 1,1-thiosulfonylation of alkenes, the reaction described here constitutes the first example of 1,6- or 1,7-thiosulfonylation of functionalized alkenes, thus offering a good complementary protocol to the existing methods. Preliminary mechanistic studies suggest a radical pathway consisting of the formation of sulfonyl radical, alkene sulfonylation, intramolecular 1,n-hydrogen atom transfer (1,n-HAT), and thiolation of acyl radical. A representative procedure for the visible-light induced remote thiolation of aldehydes initiated by the sulfonylation of alkenes with thiosulfonates is as following: To a mixture of thiosulfonates 2 (0.5 mmol), Ir(ppy)₃ (1 mol%), and K₂HPO₄ (0.5 mmol) in 4 mL of MeCN was added alkenyl aldehydes 1 (0.25 mmol) under a N₂ atmosphere. After 18 h of irradiation with 15 W blue LEDs at 25 ℃, the reaction mixture was quenched with water, extracted with EtOAc, dried over anhydrous Na₂SO₄, concentrated, and purified by column chromatography with silica gel (EtOAc/petroleum ethers=1∶5) to give products 3 or 4.

Key words: visible-light photocatalytic, sulfonylation, thiolation, thiosulfonate, remote C—H bond functionalization;