Gold(I)-Catalyzed Enantioselective Synthesis of Functionalized Indenes

Significance

The authors have developed a highly enantioselective gold-catalyzed cyclo­isomerization and alkoxycyclization of ortho-­alkynylstyrenes, which provides access to functionalized 1H-indene derivatives with excellent yields and enantioselectivities of up to 92% ee (which could be further improved to 98% ee via recrystallization). The combination of the gold complex of 3,5-xylyl-MeOBIPHEP 1 with silver salts constituted the optimized catalytic system. This method represents the first example of 5-endo-dig cyclization of ortho-alkynylstyrenes, whereas previous works reported only 6-endo cyclizations leading to naphthalene derivatives; this has become possible via directed substrate design, based on the introduction of highly substituted alkene moieties.