Enantioselective Carbon-Carbon Bond Cleavage for Biaryl Atropisomers Synthesis

Summary

Development of new synthetic strategies for enantioselective carbon-carbon and carbon-heteroatom bond formation is one of the pillars of modern organic chemistry. Whereas significant advances have been achieved in center chirality construction, catalytically asymmetric construction of axial chirality is still under development. Moreover, axially chiral molecules constructed through carbon-carbon and carbon-heteroatom bond cleavage are extremely limited. Here, we report an asymmetric synthesis of biaryl atropisomers via palladium-catalyzed chemoselective carbon-carbon cleavage of 9-aryl-9H-fluoren-9-ols. The reaction demonstrated broad substrate scope and produced the atropisomers in high yields and enantioselectivity. The ring-opening reactivity was considerably accelerated by the torsional strain created by the steric repulsion between two ortho-substituents of the biaryl skeleton in the substrates. The high enantiocontrol hinges on the evolvement of a new TADDOL-based phosphoramidite as ligand. These findings set up a new platform for the development of novel synthetic methods via asymmetric carbon-carbon cleavage.