Revisiting the CuII-Catalyzed Asymmetric Friedel-Crafts Reaction of Indole with Trifluoropyruvate.

A CuII complex of bisamidine ligand L S catalyzes the Friedel-Crafts (FC) reaction of indole with trifluoropyruvate with high generality, yielding the highly enantiomerically enriched FC adduct. Electron-rich indoles have high reactivity due to a dual activation mechanism showing second-order kinetics for CuII, whereas indoles with a soft substituent at C(4) proceed at a rate that is three orders of magnitude lower via a coordination mechanism, which reverses the sense of enantioselectivity.