Unsaturated (C(sp2/sp)–B) Boronic Acid Derivatives

Abstract

Organoboronic acids have become a very important class of compounds within modern synthetic organic chemistry and have also found utility in medicinal chemistry and material science. Although other organoboron reagents exist, such as borane and borinic acid derivatives, in the past two decades boronic acids have emerged as the predominant class of organoboron reagents. Strategies that enable the synthesis of boronic acids have gained significant attention due in part to the development of important reactions, such as the Nobel Prize winning Suzuki–Miyaura cross-coupling and the Matteson asymmetric homologation. This chapter provides an overview of the different strategies and methods that enable the synthesis of unsaturated (C(sp2/sp)–B) boronic acids and its surrogates, including the popular pinacol esters (Bpin). The preparation of organoboronic acid derivatives is subdivided into four major classes: alkenyl-, allenyl-, aryl, and alkynylboronic acids. Within those categories, the scope and limitations of common preparative methods are discussed mostly through two different general strategies; borylation of an organic fragment, or modification of a pre-borylated substrate. In the former, classical methods based on the borylation of hard organometallic precursors and alkyne hydroboration are discussed along with more recent advances in transition-metal catalyzed borylation reactions of aryl and alkenyl halides or alcohol precursors, carboboration of alkynes, and C–H borylation. The second general strategy centers on the derivatization of a borylated organic fragment, which includes alkene metathesis, hydrogenation of alkynylboronates, and cycloadditions of alkynes and dienes bearing boronic acid derivatives.