A very diastereoselective addition-elimination sequence affords cyclopentane derivatives in high enantiomeric purities. The enantiopure sulfoxide unit serves as a very efficient temporary chiral auxiliary in this tandem reaction. Interestingly, the presence of the MAD Lewis acid totally reverses the stereochemical outcome of this reaction. Several determining parameters of this sequence have been investigated: the substitution of the vinyl sulfoxide moiety, the nature of the prochiral radical, the aromatic substituent of the sulfoxide group, the tether, and the role played by different Lewis acids.