Copper-Catalyzed Enantiotopic-Group-Selective Allylation of <i>gem</i>-Diborylalkanes

Abstract

We report a copper-catalyzed enatiotopic-group-selective allylation of <i>gem</i>-diborylalkanes with allyl bromides. The combination of copper(I) bromide and H₈-BINOL derived phosphoramidite ligand proved to be the most effective catalytic system to provide various enantioenriched homoallylic boronate esters, containing a boron-substituted stereogenic center that is solely derived from <i>gem</i>-diborylalkanes, in good yields with high enantiomeric ratios under mild conditions. Experimental and theoretical studies have been conducted to elucidate the reaction mechanism, revealing how the enatiotopic-group-selective transmetalation of <i>gem</i>-diborylalkanes with chiral copper complex occurs to generate chiral α-borylalkyl-copper species for the first time. Additional synthetic applications to the synthesis of various chiral building blocks are also included.