Catalytic Enantioselective Synthesis of Planar Chiral Cyclophanes

The catalytic enantioselective synthesis of planar chiral cyclophanes has been achieved by two types of transition-metal catalysis: (1) enantioselective construction of aromatic rings by transition-metal-catalyzed [2+2+2] cycloaddition reactions; (2) enantioselective construction of ansa chains by transition-metal-catalyzed coupling reactions. The former approach has been achieved by the cationic rhodium(I)/H8-BINAP complex-catalyzed enantioselective intramolecular [2+2+2] cycloaddition of triynes, which afforded planar chiral dioxa[6]–[12]metacyclophanes with high ee values, although the yields were low. Planar chiral carba[10]–[12]paracyclophanes could also be synthesized with high yields and ee values by the cationic rhodium(I)/BDPP complex-catalyzed enantioselective intermolecular [2+2+2] cycloaddition of cyclic diynes with monoynes. On the other hand, the latter approach was achieved by the cationic rhodium(I)/BINAPHANE or palladium(II)/BINAP complex-catalyzed double C–S bond formation between dithiols and 1,4-bis(bromomethyl)benzenes, which afforded planar chiral dithia[9]–[12]paracyclophanes and dithia[3.3]paracyclophanes with varying yields and ee values.