The optical resolution of 4-amino-5-chloro-2-methyl-2,3-dihydrobenzofuran-7-carboxylic acid (I) by means of brucine in methanol gives the (+)-isomer (II), which is then condensed with the ethylamino derivative (III) by means of carbonyldiimidazole in THF to afford the amide (IV). Finally, this compound is salified with fumaric acid (V) in ethanol.

The hydrolysis of 4-acetamido-2-methyl-2,3-dihydrobenzofuran-7-carboxylic acid methyl ester (I) with NaOH gives the corresponding free acid (II), which is esterified with benzyl alcohol and carbonyldiimidazole (CDI) to the benzyl ester (III). Optical resolution of (III) by chiral HPLC yielded the 2(S)-isomer (IV), which is chlorinated with N-chlorosuccinomide (NCl) affords the 5-chloro derivative (V). The treatment of (V) with NaOH provides 4-amino-5-chloro-2(S)-methyl-2,3-dihydrobenzofuran-7-carboxylic acid (VI), which is condensed with the ethylamino derivative (VII) by means of CDI to give the amide (VIII). Finally, this compound is salified with fumaric acid (IX).