A general photo-induced wide-scope regioselective hydroboration of alkenes without using a photocatalyst or an external initiator?

Green Chemistry Pub Date: 2022-08-17 DOI: 10.1039/D2GC02313J

Abstract

Despite the recent development of boryl radical reactions, current methods to generate them by relying on photocatalysts or radical initiators cause contamination of the reaction. Herein, a novel system for generating boryl radicals has been developed without using photocatalysts or external radical initiators, and only a catalytic amount of thiol has been used. The success of this approach depends on the dual role of thiol as a proton donor and hydrogen atom transfer (HAT) catalyst. The thiol first reacts with NHC-borane to give boryl sulphides via a dehydrocoupling reaction, and then they undergo in situ cleavage of their B–S bond through photochemical reactions. The radicals obtained were later involved in a fast thiol-catalyzed HAT reaction, affording the hydroboration products. This strategy enables the regioselective hydroboration for scalable synthesis of α- or β-borylated products from many kinds of α,β-unsaturated alkenes and styrenes in good to excellent yields, with broad functional group compatibility at room temperature. The reaction could also be extended to radical-type nucleophilic addition to imines. This unprecedented protocol is anticipated to find potential application in other boryl radical-involved reactions by using boryl sulphides through photochemical reactions.

Graphical abstract: A general photo-induced wide-scope regioselective hydroboration of alkenes without using a photocatalyst or an external initiator
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