trans-Crotonyl chloride → Locostatin

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A solution of (4S)-4-benzyl-2-oxazolidinone (1.0 g, 5.6 mmol) in anhydrous THF (20 ml) was cooled to −78° C. n-BuLi (1.6 M solution in hexanes, 3.5 ml, 5.6 mmol) was added dropwise to the cooled solution. After 30 minutes, crotonyl chloride (0.59 ml, 6.2 mmol) was added to the mixture. The reaction was stirred for 30 minutes at −78° C., then warmed slowly to room temperature. The reaction mixture was quenched by addition of 4 ml saturated aqueous ammonium chloride. The resultant reaction mixture was diluted with ether, and washed with water and brine. The organic layer was dried using anhydrous Na2SO4 and evaporated under reduced pressure. Flash chromatography on a silica gel column using ethyl acetate/hexane (1/3) as eluent provided compound 1, i.e., (4S)-3-((E)-2-butenoyl)-4-benzyl-2-oxazolidinone, (1.50 g, 87%) as a white solid. m.p.: 83° C. IR (KBr): 3027, 2922, 2539, 1772, 1682, 1351, 1209 cm−1. 1H NMR (400 MHz, CDCl3): 7.36-7.15 (m, 7H, aromatic H's, CH═CH); 4.75-4.70 (m, 1H, CHN); 4.23-4.15 (m, 2H, CH2O); 3.33 (dd, 1H, J=3.3, 13.4 Hz, CHHPh); 2.79 (dd, 1H, J=9.5, 13.4 Hz, CHHPh); 1.98 (dd, 3H, J=1.0, 6.2 Hz, CH3). 13C NMR (100 MHz, CDCl3): δ 164.69, 153.51, 146.95, 135.28, 129.37, 128.86, 127.23, 121.74, 66.01, 55.20, 37.79, 18.50.

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