Ligand Controlled Highly Selective Copper-Catalyzed Borylcuprations of Allenes with Bis(pinacolato)diboron

Copper-catalyzed highly selective borylcuprations of allenes with bis(pinacolato)diboron produce two different types of alkenylboranes by applying a ligand effect. In the presence of tris(para-methoxyphenyl)phosphine [P(C6H4OMe-p)3], the reaction of aryl-1,2-dienes affords 2-alken-2-yl boronates as the only product with exclusive Z-geometry; the regioselectivity is switched to afford the 1-alken-2-yl boronates as the major products when the bidentate phosphine 2,2'-bis(diphenylphosphino)biphenyl is used as the ligand.