Allylation of Aldehydes Promoted by the Cerium(III) Chloride Heptahydrate/Sodium Iodide System: the Dependence of Regio‐ and Stereocontrol on the Reaction Conditions

The cerium(III) chloride heptahydrate/sodium iodide complex (CeCl3 ⋅ 7 H2O/NaI) acts as a useful promoter in the carbon‐carbon bond forming reaction by addition of allyltributylstannanes to aldehydes. The reaction of 2‐butenyltributylstannane shows that the regio‐ and the stereochemical outcomes depend on the reaction conditions. When the promoter is adsorbed on a solid support (aluminum oxide), a highly prevalent formation of the γ‐adduct is observed in solvent‐free conditions. Conversely, when the reaction is carried out in acetonitrile as the solvent, the α‐adduct largely prevails. In the last case, a complete stereocontrol is observed, the less stable (Z)‐isomer being obtained in high geometrical purity.