可见光催化炔硫醚的远程卤-二氟烷基化反应

Visible-Light Photocatalytic Remote Halo-difluoroalkylation of Thioalkynes

氟烷基取代的烯烃在生命科学及材料科学中具有重要价值.炔烃的氟烷基化反应为氟烷基取代烯烃的合成提供了有效方法,但是,目前大都属于1,2-双官能团化反应,而炔烃的远程氟烷基化双官能团化反应依然有待发展.以廉价易得的卤代二氟烷基试剂为自由基前体,发展了一种可见光催化的炔硫醚远程卤-二氟烷基化反应,一步构建了远端卤代的(Z)-氟烷基取代烯烃,其区域、立体和位点选择性优秀.该反应条件温和,官能团兼容性良好,同时构建了3根新的化学键,为传统方法较难合成的、热力学相对不稳定的(Z)-氟烷基取代烯烃提供了简单、高效的合成方法,也为惰性碳-氢键的直接卤代提供了新选择.初步的机理研究表明,反应经历了杂原子诱导的β-氟烷基化、1,5-氢原子迁移、单电子氧化和卤离子进攻的串联过程.

Fluoroalkylated alkenes are of significant importance in life sciences and functional materials.The fluoroalkylation of alkynes offers an efficient method for the synthesis of functionalized fluoroalkylated alkenes.However,the current methods are often limited to 1,2-difunctionalization,while the remote fluoroalkylative difunctionalization of alkynes has been rarely developed.Herein,a novel visible-light-induced remote halo-difluoroalkylation of thioalkynes is realized with difluoroalkyl halides as the radical source,forming distally halogenated(Z)-fluoroalkylated alkenes in moderate to high yields with excellent regio-,stereo-,and site-selectivity.The notable features of this reaction include the mild reaction conditions,broad substrate scope,concurrent formation of three new chemical bonds,and a thermodynamically less stable(Z)-alkene,thus enabling it a highly attractive method for organic synthesis.It represents a new advance on the direct C-H bond halogenation.Preliminary mechanistic studies indicate a cascade radical process involving the heteroatom-inducedβ-fluoroalkylation of C-C triple bonds,intramolecular 1,5-hydrogen atom transfer(1,5-HAT),single electron transfer(SET)oxidation and halide addition.