The catalytic asymmetric hydrogenation of ethyltrifluoroacetoacetate with 4,4' and 5,5'-diamBINAP-Ru(II) complexes was studied. An increased enantioselectivity was observed when hydrogenation was done in biphasic water/organic solvent conditions. Addition of acid increase the selectivity too. It was proposed an explanation based onto the keto-enol-hydrate or hemiketal equilibrium. (c) 2005 Elsevier B.V. All rights reserved.