Mechanistic Perspectives in the Regioselective Indole Addition to Unsymmetrical Silyloxyallyl Cations

Our investigations
on the reaction mechanism
to account for regioselectivity on the addition of indoles to unsymmetrical
silyloxyallyl cations are reported. Using both experimental and computational
methods, we confirmed the significance of steric effects from the
silyl ether group toward directing the inward approach of indoles,
leading to nucleophilic attack at the less substituted electrophilic
α′-carbon. The role of residual water toward accelerating
the rate of reaction is established through stabilization of the participating
silyloxyallyl cation.