Planar-Chiral Arenes via Alkyne Cyclotrimerization

Significance

Tanaka and co-workers report an enantioselective synthesis of planar-chiral arenes via an intramolecular alkyne cyclotrimerization using a cationic rhodium catalyst and (R)-(H₈)-BINAP. Although the desired chiral metacyclophane is formed in low yields due to the competing formation of an achiral orthocyclophane, the observed enantioselectivies are high. Remarkably, the yield and enantioselectivity are independent of the ansa-bridge length; [7]- to [10]metacyclophanes were easily synthesized using this method. An intermolecular variant using di-tert-butyl acetylenedicarboxylate gave the desired metacyclophane in 15% yield and 92% ee, further demonstrating the versatility of this approach.