Enantioselective Aza-Friedel–Crafts Reaction of Indoles with Ketimines Catalyzed by Chiral Potassium Binaphthyldisulfonates

The
enantioselective aza-Friedel–Crafts reaction of indoles
with low-reactive ketimines has been developed in the presence of
a chiral monopotassium binaphthyldisulfonate as a strong Brønsted
acid catalyst. A broad substrate scope was achieved, and the corresponding
3-indolylmethanamines with a chiral quaternary carbon center were
obtained in high yields with high enantioselectivities. The addition
of a catalytic amount of acetic acid considerably promoted the reaction,
and a gram-scale reaction could be achieved with reduced catalyst
loading.