alpha-Bromo-alpha-fluoro-beta-hydroxy esters, prepared as isomeric mixtures by the zinc-mediated coupling reaction of dibromo-fluoroacetate with aldehydes at -20 degreesC, were successively treated with trimethylaluminium at -15 degreesC for 0.5 h and with tributyltin hydride in the presence of a catalytic amount of triethylborane at -15 degreesC for 4 h or at -78 degreesC for 6 h to give preferentially the threo-isomers of the corresponding alpha-fluoro-beta-hydroxy esters in good yields.