Epoxidation with lanthanum-BINOL catalyst

In the presence of the sodium-containing heterobimetallic catalyst (R)-LSB (10 mol%), the reaction of enone 52 with TBHP (2 equiv) was found to give the desired epoxide with 83% ee and in 92% yield [56]. Unfortunately LSB as well as other bimetallic catalysts were not useful for many other enones. Interestingly, in marked contrast to LSB an alkali metal free lanthanoid BINOL complex, which was prepared from Ln(0- -Pr)3 and (R)-BINOL or a derivative thereof (1 or 1.25 molar equiv) in the presence of MS 4A (Scheme 17), was found to be applicable to a range of enone substrates. Regarding enones with an aryl-substitu-ent in the a-keto position, the most effective catalytic system was revealed when using a lanthanum-(.R/)-3-hydroxymethyl-BINOL complex La-51 (l-5mol%) and cumene hydroperoxide (CMHP) as oxidant. The asymmetric epoxidation proceeded with excellent enantioselectivities (ees between 85 and 94%) and yields up to 95%. 

This type of chiral lanthanum catalyst was found to be applicable for epoxidation of a range of enone substrates. Thus 35 was converted to 36 with 86% ee and in 93% yield, and 37 was transformed to 38 with 85% ee in 85% yield (Table 2, entries 1,4, and 6). The enantioselectivity of the asymmetric epoxidations could be substantially improved by the use of (/ )-3-hydroxymethyl-BINOL (32) instead of 17 (Table 2, entries 2, 3, 5, and 7). Namely, 34, 36, and 38 were obtained in excellent yields with 91, 94, and 83% ee, respectively. 

Since 2000 a few catalysts for asymmetric epoxidation based on polymer-anchored chiral l,l -bi-2-naphthol (BINOL) have been developed. Polystyrene-supported BINOL was prepared by radical copolymerization of styrene with BINOL, bearing 4-vinylbenzyloxy groups in the 3- or 6-position [96]. Immobilization of lanthanum or ytterbium was accomplished by treatment of the polymers... 

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