Substrate-Dependent Mechanisms for the Gold(I)-Catalyzed Cycloisomerization of Silyl-Tethered Enynes: A Computational Study

The gold­(I)-catalyzed alkenyl-, allyl-, and arylsilylation reactions of silyl-tethered enynes discovered by Murakami et al. provide efficient methods for the facile constructions of 1-silaindene derivatives. A comprehensive mechanistic DFT study of these reactions was carried out to better understand the experimental outcomes, and divergent and substrate-dependent mechanisms for the formations of 1-silaindene derivatives were uncovered based on the computational results. From cationic gold­(I) π-alkyne complexes, the endo-dig cyclization pathway may lead possibly to both C2- and C3-group-substituted (group = alkenyl, allyl, or aryl) 1-silaindene products, and the regioselectivity will be finally determined by the 1,2-group migration of the gold carbenoid intermediate. On the other hand, the exo-dig cyclization pathway leads only to C3-group-substituted (group = alkenyl, allyl, or aryl) 1-silaindene, in which a notable promoting effect of the bistriflimide counterion on the rearrangement of the silyl cation intermediate was disclosed. The results reported herein provide insights into aspects of regioselective cyclization, silyl-involved skeletal rearrangements, chemoselective 1,2-migration in gold carbenoids, and the dramatic counterion effect in the reactions concerned.

村上等人发现的硅基锚定炔烯的烯基、烯丙基及芳基硅基化反应，为1-硅茚衍生物的高效构建提供了简便方法。为深入理解该类反应的实验结果，研究团队开展了系统性的密度泛函理论（DFT, Density Functional Theory）机理研究；基于计算结果，揭示了1-硅茚衍生物生成的分歧性、底物依赖型反应机理。从阳离子一价金π-炔烃络合物出发，内型-dig环化路径可能同时生成C2位与C3位被烯基、烯丙基或芳基取代的1-硅茚产物，其区域选择性最终由金类卡宾中间体的1,2-基团迁移步骤决定。另一方面，外型-dig环化路径仅能得到C3位被烯基、烯丙基或芳基取代的1-硅茚产物，该路径中双三氟甲磺酰亚胺抗衡离子对硅基阳离子中间体的重排具有显著的促进作用。本文报道的研究结果，为区域选择性环化、硅基参与的骨架重排、金类卡宾的化学选择性1,2-迁移，以及相关反应中显著的抗衡离子效应等方向提供了理论见解。