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 α,β-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.