Highly Enantioselective Construction of Trifluoromethylated All-Carbon Quaternary Stereocenters via Nickel-Catalyzed Friedel-Crafts Alkylation Reaction

A highly enantioselective Friedel-Crafts alkylation reaction of indoles with beta-CF3-beta-disubstituted nitroalkenes was achieved using a Ni(ClO4)(2)-bisoxazoline complex as a catalyst, which afforded indole-bearing chiral compounds with trifluoromethylated all-carbon quaternary stereocenters in good yields with excellent enantioselectivities (up to 97% ee). The transformation of one of the products into first a trifluoromethylated tryptamine and then a trifluoromethylated tetrahydro-beta-carboline by sequential nitro reduction and Pictet-Spengler cyclization were realized with complete preservation of enantiopurity.