Tandem reactions of the yttrium(iii) catalyzed ring-opening reaction of 2,2′-diester aziridines with 3-(2-isocyanoethyl)indoles and the subsequent Friedel–Crafts/Mannich/desulfonylation were reported. A series of polycyclic spiroindolines containing tetrahydro-β-carbolines were obtained in moderate to excellent yields (56–92%) in one step under mild reaction conditions. A possible catalytic mechanism was also proposed.