Chloroacetyl chloride → (4R)-3-(Chloroacetyl)-1,3-thiazolidine-4-carboxamide

To a stirred suspension of the hydrochloride salt obtained in step III (16.5 g, 0.1 mol) in dichloromethane (200 mL) cooled to 0° C. were added Et3N (41 mL, 0.3 mol) and chloroacetyl chloride (8.8 mL, 0.11 mol). The reaction mixture was slowly warmed to room temperature and stirred for 1 h. The reaction mass was filtered through a sintered funnel, the salt bed was washed with ether, and the filtrate was evaporated under vacuum to obtain the crude product (4R)-3-(chloroacetyl)-1,3-thiazolidine-4-carboxamide (20.8 g) as viscous liquid, which was used in the next step without further purification. m/z (M+1) 209; IR cm−1 3418, 2925, 1736, 1667, 1416, 1219, 771; 1H NMR (CDCl3) 300 MHz δ 6.60-6.30 (s (br), ½H), 6.0-5.65 (s (br), ½H), 5.02 (dd, J=3.6, 6.9 Hz, 0.8H), 4.88-4.75 (m, 0.4H), 4.70 (d, J=8.8 Hz, 0.8H), 4.62 (d, J=8.8 Hz, 0.8H), 4.51 (d, J=10.0 Hz, 0.2H), 4.16 (s, 1.6H), 4.11 (s, 0.4H), 3.56 (dd, J=3.4, 11.8 Hz, 0.8H), 3.44 (dd, J=4.7, 8.0 Hz, 0.4H), 3.15 (dd, J=7.1, 11.8 Hz, 0.8H), 1.28 (s, 1.6H), 1.25 (s, 7.4H).