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  • Title: Single-isomer trisubstituted olefins from a novel reaction of (E)-beta-chloro-alpha-iodo-alpha,beta-unsaturated esters and amides.
    Author: Simard-Mercier J, Jiang JL, Ho ML, Flynn AB, Ogilvie WW.
    Journal: J Org Chem; 2008 Aug 01; 73(15):5899-906. PubMed ID: 18576689.
    Abstract:
    (E)-beta-chloro-alpha-iodo-alpha,beta-unsaturated esters are converted to single isomer trisubstituted olefins bearing three different carbon substituents by cross-coupling under reflux. Mechanistic investigations suggest that this process transfers a hydrogen from the boronic acid to the alpha-position of the substrate and then introduces an aryl group to the beta-position of the intermediate template while replacing chloride. The reaction is highly stereoselective, showing preference for the E-isomer. The process proceeds through (E)-beta-chloro-alpha-aryl-alpha,beta-unsaturated esters that are transformed efficiently into the corresponding E-products through stereoselective Suzuki-type reactions giving single isomers. The observed stereochemistry is apparently enabled by the intermediacy of a palladium allenoate. The reaction involves a catalytic cycle in which Pd(II) is reduced to Pd(0) through the formation of biaryl-coupled products.
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