Bromine-radical-induced Csp2–H difluoroalkylation of quinoxalinones and hydrazones through visible-light-promoted Csp3–Br bond homolysis

Abstract

Disclosed herein is a photosensitizer-free strategy for the direct C–H difluoroalkylation of quinoxalinones and hydrazones with bromodifluoroacylarenes via a visible-light-promoted C_sp³–Br bond homolytic pathway. This new reaction provides access to difluoroalkylated quinoxaline and hydrazone derivatives with excellent substrate generality under simple, mild, green, and metal-free conditions. This process exploits the fascinating photochemical activity of bromodifluoroacylarenes in the homolysis of C_sp³–Br bonds to form difluoroalkyl radicals and bromine radical species. The generated bromine radicals can mediate H abstraction/imine radical formation directly from quinoxalinones and hydrazones, which in turn quench the in situ-generated difluoroalkyl radicals to furnish the products. It is of note is that this is the first example of the application of bromine radicals in organic transformation via C_sp³–Br bond homolysis induced by visible light. Moreover, the minimal structural requirements for alkyl bromide-mediated photochemical C_sp³–Br bond homolysis were investigated.