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

• Published in: Organic chemistry frontiers an international journal of organic chemistry 2022-01, Vol.9 (15), p.4135-4145
• Main Authors: Chuan-Hua Qu, Huang, Run, Liu, Yuan, Liu, Tong, Gui-Ting, Song
• Format: Article
• Language: English
• Subjects: Bromine; Hydrazones; Organic chemistry; Photochemicals; Quinoxaline; Quinoxalines; Radicals; Substrates
• ISSN: 2052-4110; 2052-4110
• DOI: 10.1039/d2qo00710j

Disclosed herein is a photosensitizer-free strategy for the direct C–H difluoroalkylation of quinoxalinones and hydrazones with bromodifluoroacylarenes via a visible-light-promoted Csp3–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 Csp3–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 Csp3–Br bond homolysis induced by visible light. Moreover, the minimal structural requirements for alkyl bromide-mediated photochemical Csp3–Br bond homolysis were investigated.