Highly enantioselective Friedel–Crafts alkylation of indole and pyrrole with β,γ-unsaturated α-ketoester catalyzed by chiral dicationic palladium complex

Abstract

The chiral dicationic Pd complexes, bearing sterically demanding diphosphine ligands as Lewis acid catalysts, are shown to catalyze the asymmetric Friedel–Crafts (F–C) alkylations of indoles and pyrroles with β,γ-unsaturated α-ketoesters, to provide the F–C alkylation products with benzylic stereocenters in high yields and enantioselectivities. The reactive chelated structure, formed by the chiral dicationic Pd complex and the electrophile, would be important to gain a high level of asymmetric induction in the F–C alkylation. The F–C products can be readily functionalized to give α-hydroxy esters via catalytic asymmetric ene sequences.