Enantioselective Friedel–Crafts alkylation of indoles with β,γ-unsaturated α-ketoesters catalyzed by new squaramide-linked bisoxazoline–Zn(OTf)2 complexes

Abstract

Enantioselective Friedel–Crafts alkylation reactions of indoles with β,γ-unsaturated α-ketoesters catalyzed by novel chiral C2-symmetric squaramide-linked bisoxazoline–Zn(OTf)2 complexes were investigated. The corresponding indole ketoesters were obtained in good to excellent yields (up to 98%) and with high enantioselectivities (up to 94% ee). This is the first report on the use of chiral squaramide-linked bisoxazoline SQBOX in a catalytic enanitioselective Friedel–Crafts alkylation reaction.