“…The [6,5,5,5]-tetracyclic spiroindolines were obtained when various electrophiles were employed, which were exemplified by utilizing Michael acceptors, ,, imines, and isocyanates (Scheme B, b). However, only four examples of the generation of [6,5,5,6]-tetracyclic systems were reported through the reactions with diazoacetates, aziridines, nitrile oxide, and quinones (Scheme B, c). On the basis of our continuous interest in N -heterocycle synthesis, herein, we report a novel spirocyclization of 3-(2-isocyanoethyl)indoles with 1-sulfonyl-1,2,3-triazoles for the efficient catalyst-free synthesis of α-carboline containing a [6,5,5,6] ring skeleton (Scheme B, d).…”