Cyclic stereotriads and stereotetrads of the β-hydroxy-δ-lactone type, e.g. prelactones B and E, common in polyketides and polypropionates, are prepared via SO(2)-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-δ-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 δ-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.
Total Asymmetric Syntheses of β-Hydroxy-δ-lactones via Umpolung with Sulfur Dioxide. -A number of title compounds like (V) and (VIII) and analogously (XII) and (XIII) is prepared. The stereochemical outcome is determined by the configuration of starting materials and the reduction conditions used. -(EXNER, C. J.; LACLEF, S.; POLI, F.; TURKS, M.; VOGEL*, P.; J. Org. Chem. 76 (2011) 3, 840-845, http://dx.doi.org/10.1021/jo102035d ; Lab. Glycochem. Asymmetric Synth., Swiss Fed. Inst. Technol., CH-1015 Lausanne, Switz.; Eng.) -Jannicke
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