Rhodium( I )‐Catalyzed Hydroboration and Diboration

Rh-catalyzed hydroboration (monoboration) and diboration are powerful approaches to the synthesis of various organoboron compounds. This chapter summarizes the Rh-catalyzed boration reactions using H-BX2 and X2B-BX2. In 2004, Crudden et al. reported the Rh-catalyzed hydroboration of styrene derivatives using pinacolborane (HBpin). This regioselective reaction gives a branched benzylboronate derivatives in the presence of an appropriate Rh precatalyst and a ligand. Enantioselective hydroboration to give benzylic organoboron compounds was realized using a chiral Rh catalyst. The reaction typically gives a branched benzylic organoboron compound as a major product. The hydroboration reaction of aromatic compounds proceeds under typical reaction conditions. The chemoselective hydroboration of enynes and subsequent intramolecular cyclization give methylenecyclopentane derivatives with high enantioselectivity. The diboration reaction is a significant transformation for obtaining 1,1-, 1,2-, and 1,4-diboryl compounds. The Rh-catalyzed hydroboration of terminal alkynes is a typical approach to the synthesis of 1,1-diborylalkanes.