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) pi-alkyne complexes, the endo-dig cyclization pathway may lead possibly to both C-2- and C-3-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 C-3-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.