[3 + 2]-Annulations of -alkyl-3-substituted indoles with quinone monoketals catalysed by Brønsted acids

An organocatalytic dearomative [3 + 2]-annulation of N -alkyl-3-alkylindoles with quinone monoketals is developed. The reaction provides a mild and straightforward way to various benzofuro[2,3- b ]indolines of potential biological and pharmaceutical interest in moderate to good yields. Moreover, when 3-phenylindole, a problematic substrate in previous relevant studies, was used as the substrate under the otherwise same reaction conditions, a novel 1,2-shift of the phenyl group occurred followed by aromatization to provide 2,3-diaryl indoles useful for cancer therapy studies in moderate yields. An organocatalytic dearomative [3 + 2]-annulation of 3-alkylindoles and quinone monoketals provided benzofuro[2,3- b ]indolines, while the reaction with 3-phenylindole leads to 2,3-diarylindoles in moderate yields.