A New Synthetic Route for Silacyclopropanes: Reactions of a Bromosilylenoid with Olefins

Stable 1-bromo-1-silacyclopropanes were synthesized in high yields from the reaction of the stable bromotrisylsilylenoid 1 (trisyl = C­(SiMe₃)₃) with olefins such as styrene, trimethylvinylsilane, triethylvinylsilane, and dimethylphenylvinylsilane, a new synthetic route for silacyclopropanes. The structure of bromosilacyclopropane 5 was confirmed by X-ray analysis. In the presence of excess MeOH the phenyl-substituted bromosilacyclopropane 2 underwent regioselective ring opening to give the corresponding product 6. In contrast, the reaction of silyl-substituted bromosilacyclopropane 5 with MeOH gave only the product of nucleophilic substitution at the silicon atom, 1-methoxy-1-silacyclopropane 7, without any ring opening. Furthermore, the bromosilacyclopropane 2 extruded bromosilylene 8 through a thermal cycloreversion reaction.