Metal-free borylation of electron-rich aryl(pseudo)halides under continuous-flow photolytic conditions

• Kai Chen^a
• Man Sing Cheung^b
• Zhenyang Lin^*b
• Pengfei Li^*a

• ^a Center for Organic Chemistry, Frontier Institute of Science and Technology (FIST) and Frontier Institute of Chemistry, Xi'an Jiaotong University, 99 Yanxiang Road, Xi'an, China
• ^b Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, China

A metal-free borylation reaction of electron-rich aryl chlorides, fluorides, mesylates and phosphates under continuous-flow photolytic conditions is reported. The flow setup was designed to facilitate this process efficiently in comparison with the batch mode. Owing to its unique chemical selectivity, mild reaction conditions, good functional group tolerance and substrate scope, this reaction adds a complementary protocol to the current synthetic methods for boronic acid derivatives. The proposed reaction mechanism involves a photolytically generated triplet aryl cation, and DFT calculations suggest that the borylation product is formed in an anion-mediated single step process passing a minimum energy crossing point.

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