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Enantioselective Friedel–Crafts Alkylation Reaction of Indoles with α‑Trifluoromethylated β‑Nitrostyrenes Catalyzed by Chiral BINOL Metal Phosphate

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posted on 02.07.2019, 00:00 by Ignacio Ibáñez, Mio Kaneko, Yuto Kamei, Ryosuke Tsutsumi, Masahiro Yamanaka, Takahiko Akiyama
An efficient enantioselective Friedel–Crafts alkylation reaction of indoles with α-CF3-substituted β-nitrostyrenes is disclosed. The key to success is the use of a chiral calcium BINOL bis­(phosphate) complex as a Lewis acid catalyst. The reaction gives access to a wide variety of optically active indoles bearing trifluoromethylated all-carbon quaternary stereocenter (up to 20 examples) in high yields (up to 99%) with excellent enantioselectivities (up to 98%) under mild reaction conditions. Nonactivated α-alkyl-β-nitrostyrenes also participated in the Friedel–Crafts alkylation reaction successfully.