borylations

Borylations are a class of chemical reactions that introduce boron-containing groups into organic substrates, producing organoboron compounds such as boronic acids, boronate esters, and related boron-containing species. These compounds are widely valued in organic synthesis because they are relatively stable, tolerate many functional groups, and serve as versatile intermediates in a range of transformations, most notably cross-coupling reactions.

Several principal modes of borylation are used in practice. Hydroboration involves the syn-addition of a boron hydride across multiple bonds, such as alkenes or alkynes, to give organoboranes that can be oxidized to alcohols or converted into other boron-containing substrates. Direct C–H borylation converts C–H bonds into C–B bonds, typically using Ir or Rh catalysts and diboron reagents such as B2Pin2 to furnish alkyl or aryl boronates. Borylation of aryl or vinyl halides, often termed Miyaura borylation, uses palladium or nickel catalysts with diboron reagents to replace the halide with a boron substituent, forming aryl boronate esters.

Common boron reagents include diboron compounds like bis(pinacolato)diboron (B2Pin2) and boron hydrides such as pinacolborane (HBPin). The most widely used boron-containing products are boronic acids RB(OH)2 and boronate esters RB(OR')2, particularly the pinacol boronate ester (BPin).

Borylation products are central to many synthetic sequences because they can participate in cross-coupling reactions (such as Suzuki–Miyaura couplings), allowing rapid construction of carbon–carbon bonds. Challenges in borylation include achieving site-selectivity, functional-group tolerance, and handling air- or moisture-sensitive boron reagents, as well as the need for transition-metal catalysts.