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 Rh-II/Sc-III dual-metallic catalyst system. Control experiments revealed that Sc-III is critical to both the alkylation and annulation.

Automated summary

An enantioselective tandem Friedel-Crafts alkylation/annulation of indoles with diazoacetoacetate enones was achieved in one pot using a Rh-II/Sc-III dual-metallic catalyst system. A series of dihydrocarbazoles were obtained with moderate yields and good to excellent ee values. Control experiments confirmed the critical role of Sc-III in both alkylation and annulation processes.