Single-isomer trisubstituted olefins from a novel reaction of (E)-beta-chloro-alpha-iodo-alpha,beta-unsaturated esters and amides.
(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.
Simard-Mercier
Julie
J
Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Ontario, Canada K1N 6N5.
Jiang
Jojo Liu
JL
Ho
Michael L
ML
Flynn
Alison B
AB
Ogilvie
William W
WW