Enantioselective synthesis of fluorene derivatives by chiral N-triflyl phosphoramide catalyzed double Friedel-Crafts alkylation reaction.

A highly efficient tandem double Friedel-Crafts reaction between indoles and 2-formylbiphenyl derivatives by chiral N-triflyl phosphoramide was realized. Under mild conditions, various 9-(3-indolyl) fluorene derivatives have been obtained in good yield and up to 94% ee. Comparing to their corresponding chiral phosphoric acids, chiral N-triflyl phosphoramides catalyzed reactions led to products with opposite absolute configuration. This journal is © The Royal Society of Chemistry 2012