The addition of the PhCu, BF3.Et2O reagent to chiral dienic acetals was studied. The regioselectivity of the reaction was found to be dependent on the nature of the starting acetal. More importantly, the stereochemistry of the SN2'' reaction was found to be opposite to the one observed for the SN2' reaction. Acidic hydrolysis of the resulting enol ethers afforded the corresponding chiral ä-substituted aldehydes.