Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi 466-8555, Japan.
J Org Chem. 2013 Sep 6;78(17):8739-47. doi: 10.1021/jo401477b. Epub 2013 Aug 23.
We and others have previously reported the intermolecular umpolung reactions of Michael acceptors catalyzed by an N-heterocyclic carbene (NHC). The representative tail-to-tail dimerization of methyl methacrylate (MMA) has now been intensively investigated, leading to the following conclusions: (1) The catalysis involves the deoxy-Breslow intermediate, which is quite stable and remains active after the catalysis. (2) Addition of the intermediate to MMA and the final catalyst elimination are the rate-limiting steps. Addition of the NHC to MMA and the proton transfers are relatively very rapid. (3) The two alkenyl protons of the first MMA undergo an intermolecular transfer to C3 and C5 of the dimer. (4) The initial proton transfer is intermolecular. (5) Compared with the benzoin condensation, noticeable differences in the kinetics, reversibility, and stability of the intermediates are observed.
我们和其他人之前曾报道过迈克尔受体的分子间反转反应，该反应由 N-杂环卡宾（NHC）催化。现在已经对甲基丙烯酸甲酯（MMA）的典型尾对尾二聚化进行了深入研究，得出以下结论：（1）催化过程涉及脱氧 Breslow 中间体，该中间体非常稳定，在催化后仍然保持活性。（2）中间体与 MMA 的加成和最终催化剂消除是速率限制步骤。NHC 与 MMA 的加成和质子转移相对非常快。（3）第一个 MMA 的两个烯基质子经历了分子间转移，转移到二聚体的 C3 和 C5 上。（4）初始质子转移是分子间的。（5）与苯偶姻缩合相比，中间体的动力学、可逆性和稳定性存在显著差异。
