<i>N</i>-Heterocyclic Carbene-Catalyzed Synthesis of Ynones via C–H Alkynylation of Aldehydes with Alkynyliodonium Salts—Evidence for Alkynyl Transfer via Direct Substitution at Acetylenic Carbon
作者:Adam A. Rajkiewicz、Natalia Wojciechowska、Marcin Kalek
DOI:10.1021/acscatal.9b04394
日期:2020.1.3
the reaction was investigated by means of both experiments and density functional theory calculations. 13C-labeling and computations determined that the key alkynyl transfer step occurs via an unusual direct substitution at an acetylenic carbon, wherein an iodine-based leaving group is exchanged by a Breslow intermediate nucleophile. Moreover, kinetic studies revealed that the turnover-limiting step of
已经开发了由N-杂环卡宾(NHC)催化的炔基(芳基)碘鎓盐与醛的炔基化反应。有机催化剂和高价碘基转移试剂的应用使无金属的CH功能化和C键形成。该反应在温和的条件下,在-40°C且在胺碱的存在下进行,可提供以优异的收率获得一系列含有各种取代基的杂芳基-炔丙基酮的途径。通过实验和密度泛函理论计算研究了反应机理。13C-标记和计算确定关键的炔基转移步骤是通过乙炔碳上的异常直接取代而发生的,其中基于碘的离去基团被Breslow中间亲核试剂交换。此外,动力学研究表明,催化循环的周转限制步骤是产生Breslow中间体,而随后的C–C键形成是一个快速过程。通过计算所得的反应全自由能曲线可以完全再现和合理化这些结果,表明最大的能量跨度位于NHC催化剂的质子化形式和卡宾对醛底物的攻击的过渡态之间。