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/Nal) acts as a useful promoter in the carbon-carbon bond forming reaction by addition of allyltributylstannes to aldehydes. The reaction of 2-butenyltributylstarmane 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 gamma-adduct is observed in solvent-free conditions. Conversely, when the reaction is carried out in acetonitrile as the solvent, the a-adduct largely prevails. In the last case, a complete stereocontrol is observed, the less stable (Z)-isomer being obtained in high geometrical purity.