The dimer [Cu(OAc)2]2 promotes the addition of a thiolate and one acetate to an internal alkyne, to give a tetrasubstituted olefin in a complete stereo- and regioselective way. The determination of the mechanism by DFT methods shows the participation of Cu-stabilized radical species and how the dimer accepts the two electrons released in the addition of two nucleophiles to the alkyne through a series of cooperative changes in the oxidation states of the two copper centers. The artwork, created by S. Sierra, shows the initial blue solution of copper(II) acetate, and its structure as a dimer. For more information see the Full Paper by A. Lledós, E. P. Urriolabeitia et al. on page 13124 ff.