Copper-free and copper-promoted conjugate addition reactions of bis(triorganosilyl) zincs and tris(triorganosilyl) zincates

In the course of our investigations directed towards an asymmetric copper-catalyzed silyl transfer from bis(triorganosilyl) zincs onto alpha,beta-unsaturated carbonyl compounds, the presence of Lewis acidic lithium cations and the uncatalyzed background reaction were identified as major causes thwarting appreciable enantioselection. The latter finding underlines once more that copper is often not even required in the conjugate addition of bis(triorganosilyl) zincs and tris(triorganosilyl) zincates alike.