A DFT Study on Mechanisms and Origin of Selectivity of Phosphine-Catalyzed Vicinal Acylcyanation of Alkynoates

摘要

The mechanisms of phosphine-catalyzed vicinal acylcyanation of alkynoates have been firstly investigated by density functional theory. Both PPhMe2- and PBu3-catalyzed reactions were enumerated and studied in detail. For each reaction, three possible pathways, including the direct pathway that leads to syn-selective product and two phosphine-catalyzed reaction pathways that lead to anti- and syn-selective products respectively, were considered in this work. The calculated results indicate that the most energetically favorable pathway contains five reaction steps: the nucleophilic attack on alkynoate by phosphine, the acylation by acylcyanide, the dissociation of CN group from acylcyanide, the addition of CN group to olefin carbon of alkynoate part, and the dissociation of phosphine and product. The last two steps are the key for the anti/syn-selectivity of reactions, and our computational results can reasonably explain the experimental observations. In addition, non-covalent interaction analysis was performed for exploring the origin of the anti/syn-selectivity. Moreover, the natural bond orbital (NBO) population and global reactivity index (GRI) analyses were also carried out to disclose the role of the phosphine catalyst in this kind of reaction. This work should be helpful for chemists to understand the detailed mechanisms and predict anti/syn-selectivity of this kind of vicinal acylcyanation.