Abstract
Recent studies on the developments of the metal-catalyzed new borylation reactions by bis(pinacolato) diboron (1) are described. The 1, 4-addition of 1 to α, β-unsaturated carbonyl compounds and nitriles proceeds in the presence of a catalytic amount of CuCl and KOAc in DMF. Subsequent treatment of the reaction mixture with water produces β-boryl ketones, aldehydes, esters, and nitriles. Vinyl- and allylboron compounds are also obtained by the reactions of 1 with alkynes or allyl halides when using a stoichiometric amount of CuCl and KOAc. The aromatic C-H borylation of arenes or heteroarenes by 1 is effectively catalyzed by a combination of 1/2 [Ir (OMe) (COD)]2 and 4, 4'-di-tert-butyl-2, 2'-bipyridine in hexane. The high activity of the catalyst allows the formation of aryl- and heteroarylboron compounds in high yields at room temperature from equimolar equivalents of 1 and substrate. The direct borylation of alkylarenes by 1 catalyzed by Pd/C exclusively occurs via benzylic C-H activation to give benzylboron compounds.
