Enantioselective Synthesis of C₂-Symmetric Dimethyl Cyclohexadienedicarboxylates through Cationic Rhodium(I)/Modified-BINAP-Catalyzed [2+2+2] Cycloadditions

A cationic rhodium(I)/(S)-Tol-BINAP complex was employed to catalyze an enantioselective intramolecular [2+2+2] cycloaddition of a trans enediyne leading to a C 2-symmetric tricyclic dimethyl cyclohexadienedicarboxylate in 95% yield with 59% ee. A cationic rhodium(I)/(R)-H8-BINAP complex was employed to catalyze an intermolecular [2+2+2] cycloaddition of 1,6-diynes with dimethyl fumarate leading to C 2-symmetric bicyclic dimethyl ­cyclohexadienedicarboxylates in 35-96% yields with ee values of 82-98%.