BHA Ligands for the Synthesis of Optically Active Epoxyalcohols

(1R,2R)-N,N'-Dihydroxy-N,N'-bis(diphenylacetyl)cyclohexane-1,2-diamine (1) and (1S,2S)-N,N'-dihydroxy-N,N'-bis(diphenylacetyl)cyclohexane-1,2-diamine (2), which are called BHA ligands, are utilized in asymmetric epoxidation reactions. When an allyl alcohol is treated with a catalytic amount of vanadium-BHA complex and tert-butyl hydroperoxide (= TBHP), an epoxyalcohol is given in high yield and high enantioselectivity.¹⁾ This reaction proceeds even in the presence of water and that is an advantage compared with Sharpless-Katsuki asymmetric epoxidation, which requires strict dehydrated condition. In addition, the epoxidation proceeds in high enantioselectivities by using zirconium or hafnium as a metal species when homo- and bishomoallyl alcohols are applied.²⁾ As a result, BHA ligands are anticipated as a powerful tool of asymmetric synthesis and some researches of total syntheses of natural products using 1 or 2 have been already reported.^3,4)