Cycloheptatriene-Fused Benzosiloles: Synthesis and Reactivity

The synthesis of cycloheptatriene-fused benzosiloles is reported via a rhodium-catalyzed domino cyclopropanation/Büchner ring-expansion sequence of biphenyl-containing silyldiazomethanes. The resulting scaffold exhibits characteristic reactivity arising from a cycloheptatriene-norcaradiene equilibrium, as demonstrated by Diels-Alder trapping experiments. Oxidative conversion of the cycloheptatriene unit further provides a silicon-bridged tropylium cation, representing a cationic analogue of dibenzosilole. These results establish cycloheptatriene-fused benzosiloles as a new class of silacyclic frameworks with distinctive reactivity.