PURPOSE: To obtain the titled compound useful as pharmaceuticals, by condensing a specific thiophenol derivative with a propionic acid derivative, reacting with acetic anhydride after hydrolysis, and cyclizing the resultant threo-type propionic acid derivative with DCC.

CONSTITUTION: The objective compound of formula V, i.e. cis-2-(4'-methoxy- phenyl )-3-acetoxy-5-( N,N-dimethylaminoethyl )-2, 3-dihydro-1, 5-benzothiazepin-4- 5(H)one, is produced by (1) condensing the 2-(N,N-dimethylaminoethyl)aminothiophenol alkali metal salt of formula I (M is Na or K) with the erythro-type 3-(4- methoxy-phenyl)-3-chloro-2-hydroxypropionic acid methyl ester of formula II, (2) hydrolyzing the resultant threo-type propionic acid derivative with an alkali, (3) reacting with acetic anhydride in the presence of a base to obtain the compound of formula IV, and (4) carrying out the intramolecular cyclization reaction of the threo-type propionic acid derivative of formula IV with DCC (N,N'-dicyclohexylcarbodiimide).