The mixture of [(1S,2S)-3-chloro-2-hydroxy-1-(phenylmethyl)propyl]carbamic acid tert-butyl ester (5, 100 g), isobutyl amine (294 g), sodium carbonate (31.3 g) and water was heated to 60-65° C. and maintained for 3 hours. After completion of reaction water (200 mL) was added and distilled out excess isobutyl amine under vacuum at below 75° C. Water (800 mL) was added to the distillate, cooled to 25-35° C. and stirred for 2 hours. The obtained solid was filtered and washed with water to get title compound 4 (yield 105 g).
