Titanacyclobutenes or titanium vinyl carbene complexes? Reactivity of organotitanium species generated by the reaction of gamma-chloroallyl sulfides with a titanocene(II) reagent

摘要

The reactivity of the organotitanium species generated by the reductive titanation of gamma-chloroallyl sulfides with the titanocene(II) reagent [Cp2Ti{P(OEt)(3)}(2)] was studied. The organotitanium species formed from alpha-monosubstituted gamma-chloroallyl sulfides reacted with 1,5-diphenylpentan-3-one and styrene to produce conjugated dienes and vinyl cyclopropanes as major products, thus suggesting the formation of vinyl carbene complexes as intermediates. On the contrary, the organotitanium species generated from acyclic beta,gamma-disubstituted gamma-chloroallyl sulfides revealed titanacyclobutene-like reactivity, and their reaction with 1,5-diphenylpentan-3-one produced homoallyl alcohols. These organotitanium species did not react with styrene, but did react with dichlorophenylphosphine to afford phosphacyclobutenes. In the case of beta-monosubstituted, gamma-monosubstituted, and alpha,gamma-disubstituted gamma-chloroallyl sulfides, the organotitanium species reacted with both 1,5-diphenylpentan-3-one and styrene. The former reaction produced homoallyl alcohols and the latter gave vinyl cyclopropanes or unconjugated dienes. These results suggest that titan acyclobutenes and/or titanium vinyl carbene complexes are produced by the reductive titanation of gamma-chloroallyl sulfides depending on their substitution patterns.