No 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.

Carboxylic acid esters Q 0530Single-Isomer Trisubstituted Olefins from a Novel Reaction of (E)-β-Chloro-−α-iodo-α,β-unsaturated Esters and Amides. -Stereospecific formation of (E)-olefins takes place. The mechanism is discussed. -(SIMARD-MERCIER, J.; JIANG, J. L.; HO, M. L.; FLYNN, A. B.; OGILVIE*, W. W.; J. Org. Chem. 73 (2008) 15, 5899-5906; Dep. Chem., Univ. Ottawa, Ottawa, Ont. K1N 6N5, Can.; Eng.) -Jannicke 50-077

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