A Novel Copper(II)/Tin(II) Reagent for Aqueous Carbonyl Allylation:  In Situ Diagnostics of Reactive Organometallics in Water^†

A convenient and synthetically attractive protocol for the allylation of aldehydes using stannous chloride and catalytic cupric chloride in dichloromethane/water is described. In situ probing provides indirect (NMR, CV) and direct (MS) evidence for the copper(I)-catalyzed formation of an allyltrihalostannane intermediate in very high concentration in water.