Exploiting the σ-phylic properties of cationic gold(I) catalysts in the ring opening reactions of aziridines with indoles

A study on the SN2-type ring opening reactions of aziridines with indoles as nucleophiles is reported. Under gold(I) catalysis a great variety of tryptamine derivatives were prepared in good to excellent yields with complete stereocontrol when chiral aziridines were used. We demonstrated that cationic gold(I) catalysts are superior Lewis acids to the previously reported group 3, 12 and 13 metals in term of catalyst loading and reaction yields. Moreover, complete regioselectivity was observed for 2-phenyl-N-tosylaziridine; whereas, regioselectivity up to 10:1 ratio was observed with 2-methyl-N-tosylaziridine. Finally, a preliminary study on the dearomatization reactions giving rise to pyrroloindolines is also reported.