ortho‐Chelating Arenethiolatocopper( I ) Complexes as Versatile Catalysts in the Regioselective Cross‐Coupling of Allylic Derivatives with nBuMgI—An Example of Reversed Reactivity of Leaving Groups

The regioselectivity in the arenethiolatocopper(I)‐catalyzed crosscoupling reaction of allylic substrates was studied. It was found that allylic acetates gave highly γ‐selective reactions in Et2O at 0°C with slow addition of the Grignard reagent, whereas α‐selective reactions were obtained in THF at −30°C with fast addition of the Grignard reagent. It is proposed that the formation of an intermediate in Et2O, in which the allylic acetate coordinates in a bidentate fashion the arenethiolatocopper(I) catalyst, dramatically increases the reactivity of the leaving group and results in excellent γ‐selectivity. The remarkable observation that an allylic acetate can be made more reactive than an allylic chloride by using the arenethiolatocopper(I) catalyst 1a supports the theory of a bidentate coordination of the substrate to the catalyst through its double bond and acetate oxygen.