A general synthetic approach for the synthesis of prelactones and epi-prelactones V and E has been reported using an Evans’ aldol reaction as the key step.
Total Asymmetric Syntheses of β-Hydroxy-δ-lactones via Umpolung with Sulfur Dioxide
作者:Claudia J. Exner、Sylvain Laclef、Florent Poli、Maris Turks、Pierre Vogel
DOI:10.1021/jo102035d
日期:2011.2.4
Cyclic stereotriads and stereotetrads of the beta-hydroxy-delta-lactone type, e.g. prelactones B and E, common in polyketides and polypropionates, are prepared via SO2-induced oxyallylations of enoxysilanes with (1E,3Z)-1-(1-phenylethoxy)penta-1,3-dien-3-yl carboxylates. Using (Z)- or (E)-enoxysilanes both 4,5-cis- or 4,5-trans-delta-lactones are obtained. Depending on the reduction method applied to the obtained aldol intermediates 5,6-trans or 5,6-cis-derivatives are formed. The delta-lactones can be prepared in both their enantiomeric forms depending on the (1R)- or (1S)-configuration of the starting 1-(1-phenylethoxy)penta-1,3-dienes.
Stereoselective synthesis of polyketide fragments using a novel intramolecular Claisen-like condensation/reduction sequence
Claisen-type cleavage of the Evans-oxazolidinone with an acetateenolate followed by reduction of the resulting ketone using a borane–amine complex yielded β-hydroxy-δ-lactones as fully functionalized polyketide precursors stereoselectively. Consequently, this reaction sequence constitutes a highlypractical alternative to an acetate–aldol reaction.