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 b-silylatedb- arylthio-a,b-unsaturated ketones. The carbothiolation of PhSAc is faster than the Sonogashira coupling of PhBr and slower than that of PhI, implying that the rates of oxidative addition to Pd(0) are in the order (X=I > SAc >Br