Practical Enantioselective Synthesis of Axially Chiral Biaryl Diphosphonates and Dicarboxylates by Cationic Rhodium(I)/Segphos-Catalyzed Double [2 + 2 + 2] Cycloaddition

A cationic rhodium(I)/Segphos complex catalyzes a [2 + 2 + 2] cycloaddition of internal 1,6-diynes with a phosphonate- or ester-substituted 1,3-butadiyne leading to C2-symmetric axially chiral biaryl diphosphonates or dicarboxylates, respectively, in high yields with outstanding ee’s. The use of a phosphonate- or ester-substituted 1,3-butadiyne as a cycloaddition partner and Segphos as a ligand is crucial for the success of this transformation.