Asymmetric Transformations of Proline and 2-Piperidinecarboxylic Acid via Formation of Salts with Optically Active Tartaric Acid

The rates of racemization of optically active proline [Pro] and 2-piperidinecarboxylic acid [Pia] by using aldehydes as a catalyst tended to increase with a decrease in the acidity of the carboxylic acid used as solvent. Based on these results, the asymmetric transformations of Dl-Pro and (RS)-Pia were carried out via formation of salts with (2R, 3R)-tartaric acid to give optically pure l-Pro in over 80% yield and (R)-Pia in 70% yield. The asymmetric transformation of l-Pro was more successfully achieved by using (2S, 3S)-tartaric acid to give optically pure d-Pro in 85% yield based on the starting l-Pro.