Olefin-jr complex

The second intermediate proposed is a Cu-olefin jr-complex with an additional interaction of Mg + with the carbonyl oxygen of the enone (enoate). The formation of a jr-complex is presumably followed by intramolecular rearrangement to a Cu(III) intermediate, where Cu forms a a-bond with the -carbon of the enone (enoate), in fast equilibrium with the jr-complex. 

---