Synergistic B/Cu-Catalyzed Asymmetric Propargylic Substitution of β-Hydroxyl Ketones

A copper/borinic acid catalytic platform was developed for the asymmetric propargylic substitution of β-hydroxy ketones with propargylic carbonates. This reaction involves nucleophilic activation of β-hydroxy ketones by borinic acid to form a cyclic boron enediolate, which then reacts with a Cu-allenylidene intermediate. A series of chiral β-alkynyl ketones were prepared with high diastereoselectivity and high enantioselectivity. The utility of this method was demonstrated by a millimole-scale reaction and downstream transformations.