Studies on olefinepoxidation with t-BuOOH catalysed by dioxomolybdenum(VI) complexes of a novel chiral pyridyl alcoholate ligand

Abstract

The chiral dioxomolybdenum(VI) complexes [MoCl{(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentholato}(O)₂(THF)] and [Mo{(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentholato}₂(O)₂] have been prepared in good yields by reaction of the solvent substituted complex [MoCl₂O₂(THF)₂] with one or two equivalents of chiral 2′-pyridyl alcohol. The optically active aminoalcohol was obtained by reaction of 2-pyridyllithium with (−)-(2S,5S)-8-trimethylsilyloxymenthone. The complexes are active catalysts in the homogeneous epoxidation of cyclic and linear olefins, dienes and terpenes by t-BuOOH. They present remarkable activity and excellent product selectivity in cyclooctene epoxidation (cyclooctene oxide was obtained in quantitative yield). In the case of limonene, regioselectivity is high in favour of the epoxidation of the internal cyclic double bond. Ring opening activity was also observed for α-pinene oxide, producing campholenic aldehyde and epoxy campholenic aldehyde.