Process for the preparation of Diltiazem

A process for the preparation of (+)cis-3-acetoxy-5-2,3-dihydro-2 -(4-methoxy-phenyl)-1,5-benzothiazepin-4-(5H)-one of formula (I):

• ##STR5## and a salt thereof, which consists of the following steps:
• a) reacting under anhydrous conditions (+)-cis-3-hydroxy-2,3-dihydro-(4-methoxyphenyl)-1,5-benzothiazepin-4-(5H)- one of fomula (II):
• ##STR6## with 2-dimethylaminoethyl chloride of formula (III):
• (CH.sub.3).sub.2 N-CH.sub.2 CH.sub.2 -C1 (III)
• in the presence of sodium carbonate, to give (+)-cis-3-hydroxy-5-2,3-dihydro-2-(4-methoxyphenyl) -1,5-benzothiazepin-4-(5H)-one of formula (IV):
• ##STR7## b) acetylating said compound of formula (IV);
• c) recovering said compound (+)-cis-3-acetoxy-5-2,3-dihydro-2-(4-methoxyphenyl) 1,5-benzothiazepin-4-(5H)-one of formula (I) and when a salt thereof is desired, adding an acid to form the salt of said compound of formula I, wherein all said steps a) -c) are carried out in an aromatic solvent which is a member selected from the group consisting of toluene, xylene, chlorobenzene and dichlorobenzene.