Chiral transition-metal complexes as Brønsted-acid catalysts for the asymmetric Friedel–Crafts hydroxyalkylation of indoles

Abstract

The Friedel–Crafts reaction between 3,3,3-trifluoropyruvates and indoles is efficiently catalysed by the iridium complex [(η⁵-C₅Me₅)Ir{(R)-Prophos}(H₂O)][SbF₆]₂ (1) with up to 84% ee. Experimental data and theoretical calculations support a mechanism involving the Brønsted-acid activation of the pyruvate carbonyl by the protons of the coordinated water molecule in 1. Water is not dissociated during the process and, therefore, the catalytic reaction occurs with no direct interaction between the substrates and the metal.