The effect of vicinyl olefinic halogens on cross-coupling reactions using Pd(0) catalysis

(trans) 1-Chloro-2-iodoethylene (), (trans) 1-bromo-2-iodoethylene (), (trans) 1,2-diiodoethylene () and (cis and trans) 1,2-dibromoethylene () were reacted under Suzuki, Sonogashira and Negishi cross-coupling conditions using Pd catalysis to obtain mono coupled products. Only olefin template provided the desired coupling products reliably under all reaction conditions. Compound did not provide cross coupled products under any of the reaction conditions used. The Negishi reaction was the only one that worked for templates and . Studies indicate that oxidative addition of the most reactive carbon–halogen bond to Pd(0) is followed by elimination of the second halide, when the second halide is a bromide or an iodide. This happens to a much lesser degree when the second halogen is a chloride.