Novel radical tandem 1,6-enynes thioacylation/cyclization: Au-Pd nanoparticles catalysis versus thermal activation as a function of the substrate specificity

We studied the reactivity of 1,6-enynes with thioacetic acid (AcSH) under either thermal conditions or in the presence of catalytic amounts of supported Au or Au-Pd nanoparticles (NPs) under mild conditions. The 1,6-enynes undergo a tandem thioacylation/cyclization to original cyclic products featuring either a homoallylic thioester function or an enol thioester function depending on the substrate topology. Interestingly, the former process was found more efficient when performed in the presence of Au-Pd NPs while the latter process can be efficiently carried out under thermal conditions (100 °C). The reaction proceeds by a radical mechanism and the presence of precious metal NPs seems to stabilize the formation of free radical intermediates, as supported by experimental and theoretical results.