Synthesis and carbonylation of oxotitanocyclobutanes derived from allene cycloaddition to a monomeric titanocene oxide

Cycloaddition of monosubstituted allenes with a monomeric, base free titanocene oxide resulted in isolation and crystallographic characterization of the corresponding oxatitanacyclobutanes. In solution these compounds are a mixture of (E) and (Z) isomers and interconvert by mechanisms that are dependent on the specific substitution of the allene. Facile carbonylation of the oxatitanacyclobutanes was also observed to yield rare examples of structurally characterized oxatitanacyclopentanones. Isomerization of these species was observed in the presence of proton sources. These studies highlight the new chemistry available from synthesis of base free titanocene oxide compounds enabled by appropriate cyclopentadienyl substitution.