摘要/Abstract
有机硫化合物广泛应用于医药、农药、新材料等领域, 因此, 发展新的碳-硫键形成方法非常重要. 近年来, 烯烃的自由基砜基化反应作为一种温和、有效的有机硫化合物合成策略得到了快速发展, 其中, 烯烃的硫砜基化反应因为能够同时构建两种不同的碳-硫键成了一种非常有吸引力的碳-硫键形成方法. 以硫代磺酸酯同时作砜基化和硫化试剂, 实现了一个可见光催化烯烃砜基化启动的远程醛基碳-氢键直接硫化反应, 一步合成了6-或7-砜基取代的硫酯类化合物. 反应具有优秀的原子经济性, 产率中等到良好, 能兼容各种不同的官能团. 相比传统的烯烃1,2-或1,1-硫砜基化反应, 首次实现了官能团化烯烃的远程硫砜基化反应, 拓展了现有硫砜基化反应方法学. 初步的机理研究表明, 该反应可能经历一个可见光催化的自由基反应历程.
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;
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