Transition-Metal-Free Radical Borylation Reactions

Organoboron compounds are versatile synthons in synthetic chemistry, materials science, and medicinal chemistry. The preparation of them often requires either reactive organometallic reagents or transition metals. In recent years, transition-metal-free borylation methodologies using radical chemistry for C-B bond formation have attracted much attention and developed rapidly, which circumvents the use of preformed organometallic reagents. Various successful approaches from different radical precursors (such as carboxylic acids, amines and alcohols, which are abundant in nature) through either thermochemical, photochemical or electrochemical pathways have been developed. Therefore, in this review, we hope to provide an overview of recent advances in the discovery, development, and mechanistic study of transition-metal-free radical borylation processes.