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

Cyclisation reactions of dienyl- and enynylsilanes by carbon-carbon bond fo rmation under RCM conditions yield five-, six- and seven-membered silacyclo alkenes. The relative ease of ring formation from dienes was in the order s ix- > seven- > five-membered rings. A conjugated vinylsilacyclopentene was formed from the corresponding enyne substrate. Silaspirenes have been prepa red from silacarbacycles by the same methodology. Cyclisations effected und er radical conditions gave complimentary silacycloheptane and silacyclohept ene products. The ring closure proceeded by the endo-trig mute. (C) 2001 El sevier Science B.V. All rights reserved.