The reaction of cyclopentene oxide (I) with dimethylamine (II) gives 2-(dimethylamino)cyclopentanol (III), which is treated with methanesulfonyl chloride and NaH in THF to afford the corresponding methasulfonyl ester (IV). The condensation of (IV) with 3,4-dichloroaniline (V) in THF yields N,N-dimethyl-N'-(3,4-dichlorophenyl)cyclopentane-1,2-diamine (VI), which is acylated with propionic anhydride (A) and treated finally with maleic acid (B).