Boryl Radical Addition to Multiple Bonds in Organic Synthesis

Boryl radicals have recently contributed to the development of organoboron chemistry, but synthetic application of boryl radicals is still limited compared with other radical species. The recent development of new reagents and catalytic systems has expanded the practicality of boryl radicals in synthetic chemistry, and it has enabled addition reactions of boryl radicals to multiple bonds such as alkenes, alkynes, carbonyl groups and their derivatives. Boryl radical additions to multiple bonds can create not only novel organoboron compounds but also unusual chemical transformations. This review summarizes recently developed addition reactions of boryl radicals, which are roughly categorized by the strategy for formation of boryl radicals: (1) B–H bond cleavage and (2) B–B bond cleavage. Also, the reaction mechanism is outlined in order to understand the design and concept of each reaction.