Abstract

Organoboronic acids and esters are highly valuable building blocks in cross-coupling reactions and practical intermediates of various functional group transformations. Additionally, organoboronic acids can be utilized directly as small molecule drugs. Therefore, development of efficient methods to synthesize organoboronic compounds is of significant importance. Traditional pathways to synthesize organoboronic compounds mainly rely on electrophilic borylation of organometallic reagent and transition-metal-catalyzed borylation. Radical intermediates have unique chemical property. It is quite different from the property of polar intermediates resulted from the heterolysis of chemical bonds, and also different from the property of the organometallic compounds during transition metal catalysis. As such, borylation based on radical mechanism can realize distinctive reaction process, substrate scope, reaction selectivity, etc., and have great potential in synthesis of organoboronic compounds. In 2010, the Wang’s group first reported borylation via radical mechanism. This method realized an efficient direct conversion of anilines into aryl organoboronic esters. Inspired by this innovative work, more and more borylation methods via radical intermediates have been reported and developed as a new avenues for C―B bond formation in the past decade. A series of studies showed that organoboronic acids and esters could be efficiently constructed by the reaction of aryl/alkyl radicals with diboron compounds. In this paper, we summarized the recent development of borylation reactions via radical mechanism, including aryl and alkyl radical borylation. As for aryl radical borylation, activation of substrates containing C―N, C―O, C―S, C―X (X = halogen) bonds and carboxylic acids to C―B bond was summarized respectively. As for alkyl radical borylation, activation of substrates containing C―N, C―O, C―X (X = halogen), C―C bonds and carboxylic acids to C―B bond was summarized respectively. Finally, we made a perspective on the future development direction of this research area.

Keywords: radical chemistry; borylation reaction; diboron compounds; aryl radical; alkyl radical

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