Competitive carbothiolation and sonogashira cross-coupling in the reaction of trimethylsilylacetylene with arylthioacetates

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 beta-silylated beta-arylthio-alpha,beta-unsaturated ketones. The carbothiolation of PhSAc is faster than the Sonogashira coupling of Ph-Br andslower than that of Ph-I, implying that the rates of oxidative addition to Pd(0) are in the order (X=I > SAc >Br).