An aluminum triflate-catalyzed intramolecular reaction sequence involving protonation and Mannich-like nucleophilic addition of indoles toward the concise construction of the tetrahydropyridoA C H T U N G T R E N N U N G [1,2-a]indol-6-one skeleton is reported. This new reaction pattern employs a carbon atom as nucleophile to form a C À C bond which bears one or even two quaternary carbons and leads to the dearomatization of indoles with high atom economy.