Theoretical Studies On The Mechanisms Of Methanol-assisted Ring-opening Polymerization Of Lactide And Au-Catalyzed Cycloisomerization And Cyclization Reactions

Two parts are included in this thesis: one part is about employed density functional theory to perform a computational study of the mechanisms for methanol-assisted ring-opening polymerization of lactide, the other is about using the density functional theory studied the mechanisms of Au catalyzed cycloisomerization of tertiary allenyl carbinols and intermolecular [4+2] cycloadditions of enynes with alkynes, and they are described as follows.Part 1Stepwise addition/elimination and concerted mechanisms for the methanolysis of lactide, as a model for the initiation and propagation of ring-opening polymerization, have been investigated computationally using B3LYP/6-31 G(d, p) density functional theory calculations, with assistance from one or two ancillary methanol molecules. The results show that the extra methanol molecules acting as proton shuttles play a significant role in cyclic hydrogen-bonded clusters, and result in considerable energy savings. It is found that increasing the number of the ancillary methanol is accompanied by the reduction of the energy barrier for both stepwise and concerted mechanisms. The calculated results provide a general model that explains the mechanism of the titled reaction.Part 21) The mechanism of AuCl₃ catalyzed cycloisomerization of tertiary allenyl carbinols has been computationally addressed using DFT (B3LYP/6-31G (d) basis set for all atoms except for gold, the LANL2DZ pseudo-potential was employed for the Au). Our results indicate that the catalytically active species is Au^III in the reaction of AuCl₃ catalyzed cycloisomerization of tertiary allenyl carbinols.2) A computational study with the B3LYP density functional (6-31G (d) basis set for all atoms except for gold and stibium, the LANL2DZ pseudo-potential was employed for the Au and Sb) was carried out to elucidate the mechanisms of Au(I)-catalyzed intermolecular [4+2] cycloadditions of enynes with alkynes. Our results indicate that the mechanisms of proto-demetallation is different while using different catalyst.The innovative points in this dissertation are summarized as follows:1. For the first time using density functional method investigated the lactide ring-opening polymerization mechanisms catalysis by alcohols, the valuable results have provided reliable verification and theoretical guide for relevant experimental study, and provide new ideas for further design and development of new organocatalysis.2. The results indicate that the catalytically active species is Au^III in the reaction of AuCl₃ catalyzed cycloisomerization of tertiary allenyl carbinols.3. Our results indicate that the mechanisms of proto-demetallation is different while using different catalyst in the reaction Au(I)-catalyzed intermolecular [4+2] cycloadditions of enynes with alkynes.