Kinetic resolution of epoxy alcohols with the Sharpless Ti-isopropoxide/tartaric ester complex

When investigating the Sharpless epoxidation of enol-protected 4-hydroxy-1,2-cyclopentanediones, the ability of the asymmetric Ti(OiPr)4/tartaric ester complex to discriminate between enantiomeric epoxides formed in situ was discovered, leading to the epoxide opening reaction of only one enantiomer. This observation was used in the kinetic resolution of racemic substituted 2,3-epoxy-4-hydroxy-cyclopentanol, to afford enantiomerically enriched epoxyalcohols in good yields and with ees up to 96%.

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(4R)-3-Benzyl-2[tert-butyl(dimethyl)silyl]oxy-4-hydroxycyclopent-2-enoneC18H26O3Si[α]D25 = +122.8 (c 0.36, CHCl3), ee = 99%Source of chirality: Enzymatic kinetic resolutionAbsolute configuration: (4R)

(1R,2R,5S) 1-Benzyl-5-[tert-butyl(dimethyl)silyl]oxy-2-hydroxy-6-oxabicyclo[3.1.0]hexane-4-oneC18H26O4Si[α]D25 = +72.7 (c 1.7, CHCl3), ee = 58%Source of chirality: Sharpless kinetic resolutionAbsolute configuration (1R,2R,5S)

(2R,3R,4R)-3-Benzyl-2-((tert-butyldimethylsilyl)oxy)-3,4-dihydroxy-2-isopropoxycyclopentanoneC21H34O5Si[α]D25 = +127 (c 0.07, CHCl3), ee = 74%Source of chirality: Asymmetric ring opening with Sharpless complexAbsolute configuration (2R,3R,4R)