Gao Liuzhou, Zhang Hanyin, Liu Xueting, Wang Guoqiang, Li Shuhua
Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, P. R. China.
Dalton Trans. 2021 May 25;50(20):6982-6990. doi: 10.1039/d1dt00921d.
The mechanisms of the dearomative diborylation of pyrazines were investigated via a combination of density functional theory (DFT) calculations and experimental studies. DFT calculations revealed that a non-radical mechanism involving two successive [3,3]-σ-rearrangement-type processes is responsible for the diborylation of pyrazine with bis(pinacolato)diboron (B2pin2). However, this non-radical process is highly unfavorable for the diborylation reaction of sterically hindered pyrazine (2,3-dimethylpyrazine). For the diboration reaction of 2,3-dimethylpyrazine with B2pin2 in the presence of 2,6-dichloro-4,4'-bipyridine as the catalyst, 4,4'-bipyridine-mediated radical pathway proceeding through a B-B homolytic cleavage/boryl radical addition is preferred. Control experiments combined with kinetic studies provided supportive evidence for the proposed mechanism.
通过密度泛函理论（DFT）计算和实验研究相结合的方式，对吡嗪的去芳构化双硼化反应机理进行了研究。DFT计算表明，涉及两个连续的[3,3]-σ重排型过程的非自由基机理是吡嗪与双（频哪醇合）二硼（B2pin2）发生双硼化反应的原因。然而，这种非自由基过程对于空间位阻较大的吡嗪（2,3-二甲基吡嗪）的双硼化反应非常不利。对于在2,6-二氯-4,4'-联吡啶作为催化剂存在下2,3-二甲基吡嗪与B2pin2的双硼化反应，通过B-B均裂/硼基自由基加成进行的4,4'-联吡啶介导的自由基途径是优选的。对照实验与动力学研究相结合，为所提出的机理提供了支持证据。
