Abstract
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 °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 1e is discussed.
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