Competitive Carbothiolation and Sonogashira Cross-Coupling in the Reaction of Trimethylsilylacetylene with Arylthioacetates

Abstract

p-Bromo- or p-iodophenylthioacetate can react with trimethylsilylacetylene by simultaneous Sonogashira coupling at the halide function and addition of acetyl and arylthio moieties to the triple bond. Reaction of arylthioacetates with p-OMe, -Me, Ph and -Cl substituents, under the typical conditions of the Sonogashira coupling, leads only to the regio- and stereoselective acetylthiolation of trimethylsilylacetylene affording β-silylated-β-arylthio-α,β-unsaturated ketones. The carbothiolation of PhSAc is faster than the Sonogashira coupling of Ph−Br and slower than that of Ph−I, implying that the rates of oxidative addition to Pd(0) are in the order (X=I > SAc >Br).