Lewis acid catalysis in aqueous media: Copper(II)-catalyzed aldol and allylation reactions in a water-ethanol-toluene solution

Cu(OTf)(2) was found to be a stable Lewis acid in aqueous media and to activate carbonyl compounds effectively. Aldol reactions of silyl enol ethers with aldehydes and allylation reactions of tetraallyltin with carbonyl compounds proceeded smoothly in aqueous media, to afford the corresponding adducts in high yields. In addition, the catalyst could be easily recovered quantitatively after the reaction was completed and could be reused.