Ligand cooperativity enables highly enantioselective C–C σ-bond hydroboration of cyclopropanes

Abstract

<h2>Summary</h2> Given the utility of enantioenriched alkylboronates, asymmetric borylation has attracted substantial research interest in recent decades. Herein, a catalytic enantioselective hydroboration through desymmetrization of enantiotopic carbons in cyclopropanes involving C–C bond activation is reported. Treatment of cyclopropanes bearing an amide directing group in the presence of rhodium catalysis using HBpin as a boron source allows the construction of a series of alkyl boronates containing γ-stereogenic amines. The key to high enantioselectivity relies on two distinct ligands that act cooperatively: an exogenous monodentate chiral phosphite that induces enantioselectivity and an endogenous acetylacetonate that exerts a remarkably positive influence on the enhancement of enantioselectivity. Detailed experimental and computational studies elucidate the effect of ligand cooperativity and the key steps involving σ-bond activation process, C–B bond formation, and the absolute configuration of products.