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

Abstract

Stereoselective epoxidation of (−)-( R)-linalool by tert-butylhydroperoxide (TBHP) catalyzed by a vanadium(V) complex formed by interaction of [VO(acac) 2] or [VO(O n-Bu) 3] with a new chiral terpenoid ligand (L) is reported. Moderate diastereomeric excess (de 56%) was attained in toluene at 20 °C. 51 V , 13 C and 17 O NMR spectroscopic monitoring of the studied catalytic system showed that a new complex 1 forms quantitatively upon interaction of [VO(O n-Bu) 3] with L in CH 2Cl 2. 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±0.11 l mol −1 at room temperature and enthalpy Δ r H 298 0=−6.5±2.0 kJ mol −1 and entropy Δ r S 298 0=−20±6 J mol −1 K −1. These 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.