Arndt−Eistert homologation, 5 Curtius rearrangemen, 5 and asymmetric addition to imines 6 (ie, Staudinger reaction) were abandoned due to potential issues for scale-up associated with the manipulation of hazardous material. So we turned our attention to the most promising procedures in terms of cost, efficiency, and scalability. Aspartic acid and its derivatives were first chosen as potential starting materials as they are inexpensive and have been successfully ...