2000 stereochemistry

stereochemistry (general, optical resolution)O 0030

06 - 027The Dienolate [2,3]-Wittig Rearrangement – DiastereoselectiveSynthesis of Highly Functionalized Tertiary Alcohols. — Therearrangement of (-)-menthyl esters (E)-(I)/(E)-(II) and (Z)-(VII)/(Z)-(VIII)by treatment with base is studied in order to determine the influence of theallylic ether bound geometry as well as different substitution patterns on thereactivity and stereoselectivity. Additionally, various bases and reaction condi-tions are employed in order to evaluate their influence on the rearrangement.Under optimized conditions (1.2 equivalents LDA in THF) the mixtures of(E)-regioisomers (I)/(II) give predominantly syn products (III)/(IV) at -78 ◦Cwhereas the corresponding (Z)-isomers (VII)/(VIII) afford predominantly antiproducts (V)/(VI) at 0 ◦C. The diastereomeric excess and the yield are unaf-fected by double bond geometry of starting material. No significant difference inyield or diastereoselectivity is further observed using either mixtures of (I)/(II)or pure compounds (I) since both regioisomers give the same intermediatedienolate upon exposure to base. The chiral auxiliary can be easily removed toprovide mixtures of syn and anti diols (IX). — (HIERSEMANN, MARTIN;LAUTERBACH, CHRISTA; POLLEX, ANNETT; Eur. J. Org. Chem. (1999)11, 2713-2724; Inst. Org. Chem., TU Dresden, D-01062 Dresden, Germany; EN)

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