Asymmetric synthesis of dihydrocarbazoles through a Friedel-Crafts alkylation/annulation sequential reaction of indoles.

An enantioselective tandem Friedel-Crafts alkylation/annulation of indoles with diazoacetoacetate enones is realized in one pot. A series of dihydrocarbazoles were obtained in moderate yields with good to excellent ee values by using a RhII/ScIII dual-metallic catalyst system. Control experiments revealed that ScIII is critical to both the alkylation and annulation.