Alkylthio substituted tricarbonyl(η6-arene)chromium(0) complexes as substrates for asymmetric oxidation

Article abstract of DOI:10.1016/0957-4166(94)80093-6

Oxidation of methylthio substituted tricarbonyl(η⁶-arene)chromium(0) complexes with Ti(OPr(i))₄/ diethyl tartrate H₂O/ cumene hydroperoxide (2:4:2:1.3) gives methylsulfinyl substituted tricarbonyl(η⁶-arene)chromium(0) complexes in 60-73% yield and 81-86% e.e. (29-60% yield and 90 ≥ 95% e.e. after crystallisation); diethyl tartrate gives higher optical and chemical yields than dimethyl or diisopropyl tartrates and the reaction conditions are ineffective for other alkylthio and arylthio substituents: diethyl L-(+)-tartrate and diethyl D-(-)-tartrate lead to complexes of R and S configuration respectively; although an attempted kinetic resolution of tricarbonyl[η⁶-(melhylsulfinyl)benzene] was unsuccessful, subjecting tricarbonyl[η⁶-1-melhyl-2-(methylthio)benzene]chromium(0) to kinetic resolution conditions led to the isolation of recovered starting material and the corresponding sulfinyl substituted complex with enantiomeric excesses of 59 and 60% respectively.