Stereoselective oxidation of linalool with tert-butyl hydroperoxide, catalyzed by a vanadium(V) complex with a chiral terpenoid ligand

Stereoselective epoxidation of (-)-(R)-linalool by tert-butylhydroperoxide (TBHP) catalyzed by a vanadium(V) complex formed by interaction of [VO(acac)(2)] or [VO(On-Bu)(3)] with a new chiral terpenoid ligand (L) is reported. Moderate diastereomeric excess (de 56%) was attained in toluene at 20 degreesC. V-51, C-13 and O-17 NMR spectroscopic monitoring of the studied catalytic system showed that a new complex 1 forms quantitatively upon interaction of [VO(On-Bu)(3)] with L in CH2O2. Compound 1 is a mononuclear complex of vanadium(V), which incorporates the tridentate chiral ligand L, as well as V=O moieties. It has been shown that TBHP binds to 1 giving a 1.TBHP adduct with the association constant K = 1.36 +/- 0.111 mol(-1) at room temperature and enthalpy Delta(r) H-298(0) = -6.5 +/- 2.0 kJ mol(-1) and entropy Delta(r) S-298(0) = -20 +/- 6 J mol(-1) K-1. These 29 thermodynamic parameters are typical for outer sphere complexes (OSCs). Adduct 1 .TBHP is suggested to be a precursor of the active intermediate of the stereoselective epoxidation process. (C) 2002 Elsevier Science B.V. All rights reserved.