Desymmetrization of a Centrosymmetric Diepoxide: Efficient Synthesis of a Key Intermediate in a Total Synthesis of Hemibrevetoxin B
作者:Joanne M. Holland、Mark Lewis、Adam Nelson
DOI:10.1021/jo026456b
日期:2003.2.1
The preparation of an established intermediate in a totalsynthesis of hemibrevetoxinB is described. The acid-catalyzed cyclization of trans-4,5-epoxyoctane-2,7-dione exhibited a valuable mixture of kinetic and thermodynamic control: stereospecific epoxide opening was followed by equilibration of the products to provide the required trans-fused octahydropyrano[3,2-b]pyran ring system. Two-directional
Desymmetrisation of a Centrosymmetric Molecule by Carbon–Carbon Bond Formation: Asymmetric Aldol Reactions of a Centrosymmetric Dialdehyde
作者:Karen Dodd、Daniel Morton、Stephen Worden、Robert Narquizian、Adam Nelson
DOI:10.1002/chem.200700277
日期:2007.7.6
The desymmetrisation of centrosymmetric molecules by enantioselective carbon-carbon bond formation has been reported for the first time. A bimetallic zinc catalyst developed by Trost was exploited in the desymmetrisation of a centrosymmetric dialdehyde. The approach was successful with a range of ketone nucleophiles and was uniformly highly diastereoselective (>98:<2). The yield and the enantioselectivity
of molecular symmetry can greatly improve the efficiency of syntheses. The symmetry embedded in the centrosymmetric AB dioxepane fragment of hemibrevetoxinB was exploited for the first time in the preparation of an established intermediate in its totalsynthesis. Desymmetrization of the centrosymmetric diepoxide 1 by enantioselective epoxide hydrolysis followed by acetonization gave the known synthetic