Enhanced efficiency of recyclable C3-symmetric cinchonine-squaramides in the asymmetric Friedel-Crafts reaction of indoles with alkyl trifluoropyruvate

The highly enantioselective Friedel-Crafts reaction of indoles with trifluoropyruvate catalyzed by a C-3-symmetric cinchonine-squaramide is reported. A wide variety of trifluoromethylated indole derivatives were obtained in high yields and with excellent enantioselectivities (99% and up to > 99% ee). Moreover the C-3 catalyst can be easily recovered and was used five times. (C) 2012 Elsevier Ltd. All rights reserved.