A regioselective one-pot aza-Friedel-Crafts reaction for primary, secondary and tertiary anilines using a heterogeneous catalyst

A one-pot multicomponent aza-Friedel-Crafts reaction was performed under green, neat and heterogeneous conditions in the presence of 1.25 mmol% of 30% w/w silicotungstic acid supported on Amberlyst 15 beads. In a yet unprecedented attempt, both primary and secondary anilines could provide the 3-substituted indole product in good to excellent yields usually at room temperature whilst tertiary anilines gave moderate results. Interestingly all reactions proceeded regioselectively via two separate C-C bond forming reactions rather than C-C and C-N bond forming steps. The catalyst is easy, safe and environmentally-benign to prepare, completely recoverable and recyclable up to 5 times.