A novel process for producing an optically active (E)-7-[2-cyclopropyl-4-(4-fluorophenyl quinolin-3-yl]-5-hydroxy-3-oxohept-6-enoic acid ester of formula (III) which is important as an intermediate for synthesizing medicines, comprises reacting 1,3-bis(trimethylsilyloxy)-1-alkoxybuta-1,3-diene of formula (I) with (E)-3-[2-cyclopropyl-4-(4-fluorophenyl)-quinolin-3-yl]-prop-2-en-1-al of formula (II) in the presence of an optically active binaphthol-titanium complex obtained from 1,1'-bi-2-naphthol with titanium tetraisopropoxide, a metal salt and an amine, and then subjecting the reaction product to desilylation ##STR00001##