A new process for manufacturing entacapone comprising reacting 3,4-dihydroxy-5-nitrobenzaldehyde with N,N-diethyl-2-cyanoacetamide in the presence of a catalyst in a C 4 to 8 alcohol at reduced pressure and at a temperature of at least 70 °C, cooling the mixture to a temperature of 30 °C or below, seeding the mixture with N,N-diethyl-2-cyano-3-(3,4-dihydroxy-5-nitrophenyl)acrylamide comprising at least 10 % of the Z-isomer by weight in the seeding crystals, cooling the mixture to a temperature of 5 °C or below, isolating the crystallized product and converting the obtained mixture of the E- and Z-isomers of N,N-diethyl-2-cyano-3-(3,4-dihydroxy-5-nitrophenyl)acrylamide to the E-isomer (entacapone).
