Intramolecular Friedel-Crafts alkylation with a silylium-ion-activated cyclopropyl group: formation of tricyclic ring systems from benzyl-substituted vinylcyclopropanes and hydrosilanes

A trityl-cation-initiated annulation of benzyl-substituted vinylcyclopropanes (VCPs) with hydrosilanes is reported. Two Si-C(sp(3)) bonds and one C(sp(2))-C(sp(3)) bond are formed in this process where an intramolecular 6-endo-tet Friedel-Crafts alkylation of a silylium-ion-activated cyclopropane ring is the rate-determining key step. The reaction mechanism is proposed based on computations and is in agreement with experimental observations. The new reaction leads to an unprecedented silicon-containing 6/6/5-fused ring system. A phenethyl-substituted VCP derivative yields another unknown tricycle having 6/6/6 ring fusion by reacting in a related but different way involving a 6-exo-tet ring closure.

Automated summary

A trityl-cation-initiated annulation of benzyl-substituted vinylcyclopropanes with hydrosilanes has been reported, leading to the formation of new Si-C(sp(3)) and C(sp(2))-C(sp(3)) bonds through intramolecular reactions. The reaction mechanism proposed based on computations is in agreement with experimental observations, resulting in the formation of unprecedented silicon-containing fused ring systems. Another tricycle with a 6/6/6 ring fusion structure was obtained from a phenethyl-substituted VCP derivative through a related but different reaction pathway.