Brønsted Acid Catalysis: Friedel-Crafts Alkylation with Chiral Disulfonimides

Significance

Lee and co-workers report the asymmetric Friedel-Crafts alkylation of indoles with tosylated arylimines. The reaction is catalyzed by the binaphthyl-based disulfonimide A, which is proposed to act as hydrogen-bridge donor and acceptor, thereby assembling the substrates within its chiral environment and favoring the si-facial attack. While unsubstituted indole and derivates with electron-donating groups reacted with equally high enantioselectivities, electron-withdrawing groups were found to be detrimental to the enantioselectivity. When other sulfonyl groups were employed instead of the tosyl group, reduced yields and/or enantioselectivities were observed in all cases.