ECD Calculation:

The theoretical calculations of compounds1−4 were performed using Gaussian 09.Conformational analysis wasinitially carried out using Maestro7.5 conformational searching,together with the OPLS_2005 molecular mechanics methods. The optimized conformation geometries, important dihedral angles,thermodynamic parameters, and populations of all conformations are provided in the Supporting Information (Tables S1−4). The OPLS_2005 conformers were then optimized at the B3LYP/6-31G(d, p) level. Room-temperature equilibrium populations were calculated according to the Boltzmann distribution law. The theoretical calculation of ECD was performed using TDDFT
6,7 at the B3LYP/6-31G (d, p) level in MeOH with the PCM model and in the gas phase, respectively. The ECD spectra of compounds1−4were obtained by weighing the Boltzmann distribution rate of each geometric conformation.

MO Analysis:

The orbital information (NBO plotfiles) was generated using the NBO program of Gaussian 09. The predominantly populated conformers were selected for MO analysis.NBO plotfiles were used to generate corresponding Gaussian-type gridfiles using Multiwfn 2.4.After that, the isosurface of generated grid data was generated by VMD software.