The condensation of aromatic aldehydes 1 and D-penicillamine (2) in aqueous methanol gives (4S)-2-aryl-5, 5-dimethyl-4-thia-zolidinecarboxylic acids 3 with alternating diastereoselectivity in position 2. Acetylation of the products with acetic anhydride in pyridine or in water gives rise to (ZS, 4S)-3-acetyl-2-aryl-5, 5-dimethyl-4-thiazolidinecarboxylic acids 5. Use of a