Site- and Enantioselective Homobenzylic C(sp³)–H Borylation via Dehydrogenation of Alkyl Chains

A one-pot, dehydrogenation-based Ir/Co/Cu triple catalysis has been developed for formal asymmetric borylation of homobenzylic C(sp³)-H bonds, furnishing enantioenriched organoboronates with a β-stereocenter directly from simple arylalkanes. Mechanistic studies indicate that the Ir catalyst is responsible for dehydrogenation of arylalkanes to 1-arylalkenes, followed by Cu-catalyzed regio- and enantioselective protoboration of (<i>E</i>)-arylalkenes; the introduction of Co-catalyzed stereoisomerization of the (<i>Z</i>)-alkenes to (<i>E</i>)-isomers was found to have a beneficial effect on the productivity and enantioselectivity.