A great deal of effort has gone into the research, development and application of mixed organocuprate(I) reagents [R T R NT CuLi]. [1][2][3][4][5][6][7] These "mixed cuprates" contain one group R T that is transferred to a substrate and a second, nontransferred group R NT (sometimes called a "dummy ligand") that is assumed to be inert under the reaction conditions. They were introduced in order to solve the efficiency problem of homocuprates R 2 CuLi (Gilman reagents), which only transfer one equivalent of the R-group in most applications. Outstanding examples include thienyl (Th), [2] cyano, [3] alkynyl, [4] thiolato, [5] trimethylsilylmethyl, [6] and phosphido [7] groups.We have found that upon addition of typical a,bunsaturated ketones, esters, nitriles, or sulfones, these mixed cuprates give p complexes that exhibit a remarkable orientation effect in which R T is cis to the site of the usual addition reaction, for example, the b-carbon in a,b-unsaturated carbonyl compounds 1 (Scheme 1). Complexes with C À N and C À S double bonds also display this effect. The selforganization we report here substantially reduces the com-plexity of mixed organocuprate reagents, and it is essential for a complete understanding of their reaction mechanisms.