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

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 beta,gamma-unsaturated alpha-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 alpha-hydroxy esters via catalytic asymmetric ene sequences. (C) 2011 Elsevier Ltd. All rights reserved.