Computational Details
All theoretical calculations were carried out by using theGaussian09 suit of program.63 Structures of all stationary points, including the reactants, products, transition states and intermediates, were fully optimized by using the M06-2X functional64-66 and the 6-31G(d, p) basis set67,68under gas phase (Level A ). The harmonic frequency calculations were performed at the same level with the temperature set as 303.15 K and the pressure as 1 atm according to the experimental report. All reactants, products, and intermediates were corroborated to have no imaginary frequency while each transition state to have one and only one imaginary frequency. The same level of intrinsic reaction coordinate calculations (IRC)69,70were carried out to confirm each transition state linked the expected reactant and product. Based on the optimized structures, all energies were refined by single-point calculations at the M06-2X/6-311++G(d, p)71 level of theory, with the solvent effects of DMSO simulated by Truhlar’s SMD72,73model (Level B ). All energies discussed in this paper were calculated by adding the single-point energies obtained at Level B to the thermal corrections of the Gibbs free energies calculated atLevel A .