The reduction of enantiopure β-enamino esters 1 with sodium triacetoxyborohydride in acetic acid is described. This occurs with good diastereo-and enantioselectivity to yield β- amino esters 2 and 3 (after hydrogenolysis of the N-chiral group). A model is reported for the origin of the stereoselectivity through an enol ester-diacetoxyborohydride 6, which affords the intramolecular reduction. By choosing the appropriate chiral amine, this procedure ...