The effects of the solvent and the ligand chirality on the regioselectivity of alkene oxidative esterification by PdII carboxylates

Article abstract of DOI:10.1007/BF02494811

The effects of the solvent and the ligand chirality on the regioselectivity of oxidative esterificanon of propylene and cyclohexene by Pd^II carboxylates were studied using achiral (MeCO₂^-, Me₂CHCH₂CO₂^-), racemic ((±)-CF₃CF₂CF₂OC*F(CF₃) CO₂^-) and chiral ((S)-(+)-MeC*H(Et)CO₂^-, (+)-CF₃CF₂CF₂OC*F(CF₃)CO₂ ^-) carboxylate ligands. The oxidation of alkenes in aprotic media (CHCl₃, CH₂C1₂, CO₂, THF) affords mainly allylic esters (in the case of cyclohexene also homoallylic esters) and the oxidative esterification at the vinylic position is absent. In weakly solvating media (CHCl₃, CH₂Cl₂) the regioselectivity of cyclohexene oxidation (the allyl to homoallyl ratio) increases substantially on going from achiral or racemic acido ligands to chiral acido ligands. In a more donor medium (THF) the ligand chirality effect almost vanishes. The effects of the ligand chirality and the nature of the solvent on the mechanism of alkene oxidation by Pd^II complexes are discussed.