A convenient method to synthesize 1, 4-thiazane-3-carboxylic acid derivatives was established. Condensation of L-cysteine methyl ester (2a) with monochloroacetone (3a) followed by reduction with sodium borohydride yielded methyl (3R, 5S)-5-methyl-1, 4-thiazane-3-carboxylate (6a) and its (5R)-methyl isomer (7a) in a ratio of 3.1 : 1. The use of cysteine isopropyl ester (2c) instead of methyl ester (2a) gave the corresponding (5S)-methyl isomer (6e) more stereoselectively. The reaction of chloromethyl ethyl ketone (3b) or α-bromoacetophenone (3c) with 2a gave the corresponding 5-substituted-1, 4-thiazane-3-carboxylates. Hydrolysis and oxidation of 6a yielded cycloalliin (1a).