Design of optically active hydroxamic acids as ligands in vanadium-catalyzed asymmetric epoxidation

New optically active hydroxamic acids bearing a 1,1'-binaphthyl group were prepared as ligands in a vanadium-catalyzed asymmetric epoxidation. The feature of these hydroxamic acids is a sterically hindered ligand. The asymmetric epoxidation with good selectivity and reactivity can be established by using VO(O-i-Pr)(3) (5 mol%) and a small excess amount of ligand (7.5 mol%) with triphenylmethyl hydroperoxide (TrOOH) in toluene at -20 degrees C. Disubstituted allyl alcohols were epoxidized more rapidly than mono- or tri-substituted allyl alcohols, and were obtained in good to high enantioselectivities (48-94%ee). The transition state based on X-ray crystal structure of le is discussed.