Boron‐Mediated Radical Reactions

Abstract This chapter focuses on the use of boron‐containing reagents in radical reactions. In all reactions presented here, boron is playing a key role in the radical process either by being part of the radical process or by influencing the reactivity of the radical and nonradical species. The diversity of radical chemistry involving organoboron species is spectacular. They represent a unique source of radicals for chain reactions allowing for instance efficient radical initiation at low temperature and generation of a broad range of functionalized alkyl radicals from easily prepared organoboranes. Recent developments in redox chemistry including photoredox catalysis, electrochemistry, and single‐electron‐transfer processes have allowed the generation of alkyl and aryl radicals from stable organoboron derivatives such as alkyl‐ and aryl‐trifluoroborates. A broad range of synthetic applications such as radical cascade processes, multicomponent reactions, and cross‐coupling reactions in the presence of suitable metals are possible. Besides radical generation, boron‐containing radical precursors and radical traps are becoming of increasing importance to prepare building blocks enclosing a boron moiety suitable for further functionalization. Merging radical processes with classical boron chemistry including Suzuki–Miyaura‐type cross‐coupling processes; homologation via 1,2‐metallate rearrangement; and conversions to alcohols, amines, and related compounds offers unique opportunities for applications in organic synthesis.