Silylium-Ion-Promoted Ring-Opening Hydrosilylation and Disilylation of Unactivated Cyclopropanes

A silylium-ion-promoted ring-opening hydrosilylation of unactivated cyclopropanes is reported. The reaction is facilitated by the gamma-silicon effect, and the regioselectivity is influenced by various stabilizing effects on the carbenium-ion intermediates, including the beta-silicon effect. The experimental observations are in accord with the computed reaction mechanism. The work also showcases the ability of silylium ions to isomerize cyclopropyl to allyl groups, and the resulting alpha-olefins engage in a silylium-ion-mediated disilylation with hexamethyldisilane.