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 ringformation from dienes was in the order six->seven->five-memberedrings. A conjugated vinylsilacyclopentene was formed from the corresponding enyne substrate. Silaspirenes have been prepared from silacarbacycles by the