Metathetical cyclization of dienes containing P, O, S or Si heteroatoms by a cyclometallated aryloxy-carbene of tungsten. Inhibition effects and steric constraints: A review

Intramolecular metathesis of various diallyl compounds containing the O, S, Si or P hetero element was achieved with good yields by using the cyclometallated carbene complex W(OAr) (OAr)(CHMe₃)Cl(OEt₂). Unsubstituted diallyl ether is converted into 2,5-dihydrofuran; diallyl sulfide is converted into 2,5-dihydrothiophen; diallyl-phenyl phosphine is converted into phenyl-2,5-phospholen and diallyl dimethyl- or diphenylsilanes are converted into the corresponding silacyclopentenes. Metathesis reaction of methyl-substituted diallyl-sulfides shows that steric effects are very important. These steric effects are also well seen by addition of di-n-propyl or di-i-propyl sulfides during the metathesis reaction of diallyl sulfide. Indeed, only the former compound inhibit the reaction, showing that there is an important steric crowding around the tungsten atom.