Atroposelective Construction of Carbon-Boron Axial Chirality through Rh-Catalyzed [2+2+2] Cycloaddition

Axially chiral compounds have widespread applications in many fields. While significant progress has been made for the asymmetric synthesis of atropisomers consisting of C-C bonds, an efficient approach for the construction of C-B atropisomers is still lacking. Herein, we report a practical method for atroposelective synthesis of axially chiral arylboron compounds through Rh-catalyzed [2 + 2 + 2] cycloaddition. The reaction exhibits a broad substrate scope and good functional group tolerance, thus providing an efficient protocol to access a variety of C-B atropisomers in high yields and good enantiocontrol. The utility of these C-B atropisomers has been adequately demonstrated by versatile transformations into highly valuable compounds such as chiral phosphine ligands and fluorescent molecules. Mechanistic experiments and DFT calculations have provided insights into the reaction mechanism as well as the origin of enantiocontrol.