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 β-CF3-β-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-β-carboline by sequential nitro reduction and Pictet–Spengler cyclization were realized with complete preservation of enantiopurity.