Chiral phosphoric acid-catalyzed enantioselective aza-Friedel-Crafts reaction of indoles

A highly enantioselective 1,2-aza-Friedel-Crafts reaction of N-tert-butyldimethylsilylindole with N-tert-butoxycarbonyl aromatic imines is demonstrated using a BINOL-derived monophosphoric acid catalyst. The present approach provides efficient access to 3-indolylmethaneamines with aryl substituents in excellent enantioselectivities (up to 98% ee). An inversion in the sense of enantioselection was found between monophosphoric acid catalysts bearing different substituents introduced at the 3,3′-position of binaphthyl backbone. We also calculated the three-dimensional structure of the monophosphoric acid catalysts to speculate on the inversion of the stereochemical outcome.