Synthesis of silacycloalkenes and silaspirenes by Ru(II)-catalyzed ring-closing metathesis reactions

Cyclisation reactions of dienyl- and enynylsilanes by carbon–carbon bond formation under RCM conditions yield five-, six- and seven-membered silacycloalkenes. The relative ease of ring formation from dienes was in the order six->seven->five-membered rings. A conjugated vinylsilacyclopentene was formed from the corresponding enyne substrate. Silaspirenes have been prepared from silacarbacycles by the same methodology. Cyclisations effected under radical conditions gave complimentary silacycloheptane and silacycloheptene products. The ring closure proceeded by the endo-trig route.