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.