The reaction mechanism for N-methylindole and keto ester catalyzed by InX 3 (X＝F, Br) was studied by the density functional theory (DFT). The geometries and the frequencies of reactants, intermediates, transition states, and products have been calculated at the B3LYP/6-31＋G(d, p) level, dichloroethane (DCE) is used as a solvent and the LanL2DZ basis has been used for In atom. Transition states have been confirmed by the corresponding vibration analysis and intrinsic reaction coordinate (IRC). In addition, nature bond orbital (NBO) and atoms in molecules (AIM) theories have been used to analyze orbital interactions and bond natures. The results showed that the activation energies of rate-determining steps in which N-methylindole reacted with keto ester to form 1,2-adduct and 1,4-adduct were 25.62 and 12.52 kcal/mol catalyzed by InF 3 while those were 26.87 and 13.95 kcal/mol when the reaction was catalyzed by InBr 3 under the same conditions. Comparing the results of our research, InF 3 can effectively catalyze the reaction, and the 1,4-adduct was more likely to be produced. The final result of our theory study agreed with the experimental data, meanwhile, self-consistent reaction field (SCRF) was carried out using the polarized continuum model (PCM) at the same theoretical level for geometry optimizations and frequency calculations in five different salvations. We predicted that the productivity to form 1,4-adduct was more higher catalyzed by InF 3 in the solvent of dimethyl sulfoxide (DMSO).

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