ɑ-Amino acids can be converted to the corresponding ɑ-chloro acids with a high degree of retention of configuration, by diazotization in the presence of HCl: J. Am. Chem. Soc., 76, 6054 (1954). The intermediate is thought to be a rigid oxiranone which prevents racemization. For an improved technique and list of examples, see: Org. Synth. Coll., 8, 119 (1993).
