Hydroboration

Abstract

The hydroboration reaction and transformations of its organoborane products are described. The mechanism and the chemo‐, regio‐, and stereoselectivity of the uncatalyzed and catalyzed hydroboration reaction are presented, as well as the synthesis and characteristics of the most common hydroborating agents. Transformations of organoboranes may involve carbon–heteroatom bond formation and lead to stereoselective synthesis of organic halides, amines, aziridines, sulfur, selenium, mercury, and zinc compounds. Hydroboration–protonolysis is a nonocatalytic method for cis hydrogenation of multiple bonds. Hydroboration–oxidation is a standard method for cis‐anti‐Markovnikov hydroxylation of multiple bonds, whereas the catalyzed hydroboration may lead to Markovnikov hydroxylation. Contrathermodynamic isomerization of olefins is discussed. Carbon–carbon bond formation can be accomplished by transformation of organoboranes through coupling of groups attached to boron, cross‐coupling of organoboranes with organic halides and triflates, organoborate rearrangements providing access to alkynes, dienes, and enynes. Single‐carbon insertion reactions, make possible homologation of organoboranes. Other transformations include α‐alkylation of carbonyl compounds, the boron Wittig reaction, concerted reactions of allylic and vinylic boranes, allylboration, allenylboration and propargylboration of aldehydes leading to stereodefined allylic, homoallylic, and allenyl alcohols. The synthesis of boron‐containing polymers and isotopically labeled compounds is covered. Asymmetric synthesis via chiral organoboranes and stereodirected enolboration–aldolization is described.

Nickel-Catalyzed Coupling Reactions of Alkyl Electrophiles, Including Unactivated Tertiary Halides, To Generate Carbon–Boron Bonds

“…Alkylboron compounds have a broad spectrum of applications, ranging from cancer medicine (bortezomib, marketed as Velcade by Millennium Pharmaceuticals) to organometallic partners in cross-coupling reactions . Alkylboranes are most often prepared via the hydroboration of olefins or the transmetalation of highly reactive organolithium/organomagnesium reagents with electrophilic boron species . These methods have significant limitations, such as a regioselectivity issue in the case of hydroborations of many internal olefins and functional-group incompatibility in the case of transmetalations.…”