Synthesis of Indolylindolines Mediated by tert-BuNH2

An improved synthesis of N1-carbomethoxylated indolylindolines 2 from 5-substituted indoles 1, by replacing the previously employed strong acids or toxic metals with t-BuNH2/MeOCOCl in CH2Cl2/H2O, is described. The substituent effect of electron donor or acceptor groups was examined, revealing that electron-deficient indoles are less reactive to dimerization than electron-rich indoles, with 5-cyano and 5-nitroindoles leading to no reaction. A dynamic process caused by the restricted rotation of the N-CO2Me bond of 2 was evidenced by 1H NMR measurements.