Investigation into the Allylation Reactions of Aldehydes Promoted by the CeCl₃·7H₂O−NaI System as a Lewis Acid

The Lewis acid promoted allylation of aldehydes has become an important carbon−carbon bond forming reaction in organic chemistry. In this context, we have developed an alternative over existing catalytic processes, wherein aldehydes are subject in acetonitrile to reaction of allylation with allyltributylstannane in the presence of 1.0 equiv of cerium(III) chloride heptahydrate (CeCl₃·7H₂O), an inexpensive and mild Lewis acid. The allylation has been accelerated by using an inorganic iodide as a cocatalyst, and various iodide salts were examined. The procedure must use allylstannane reagent instead of allylsilane reagent, desirable for environmental reasons, but high chemoselectivity was observed, and this is opposite the results obtained with other classical Lewis acids such as TiCl₄ and Et₂O·BF₃.