(Diethylamino)sulfur trifluoride → 1,2-Pyrrolidinedicarboxylic acid, 4-fluoro-, 1-(1,1-dimethylethyl) 2-methyl ester, (2R,4R)-rel-

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Reaction Steps

To a stirred solution of compound obtained in step II (24.5 g, 0.1 mol) in 1,2-dichloroethane (300 mL) cooled to −10° C. was added diethylaminosulfur trifluoride (19.7 mL, 0.15 mol) over a period of 30 minutes. The reaction mixture was stirred at this temperature for 1 h then at room temperature for 16 h. The reaction mixture was quenched by adding mixture of crushed ice (300 g) and solid NaHCO3 (25.2 g, 0.3 mol). The two layers were separated and the aqueous layer was extracted with dichloromethane. The combined organic layer was washed with brine, dried over anhydrous Na2SO4, and the solvent was removed under reduced pressure to obtain 1-tert-butyl 2-methyl (2S,4S)-4-fluoropyrrolidine-1,2-dicarboxylate as a viscous liquid (24.7 g) in 100% yield. [α]D −53.3, (c, 1.0, CHCl3). m/z (M+1) 248; 1H NMR (CDCl3) 300 MHz δ 5.20 (ddd, J=3.8, 3.8, 49.1 Hz, 1H), 4.55 (d, J=9.5 Hz, ½H), 4.42 (d, J=8.9 Hz, ½H), 3.90-3.55 (m, 2H), 3.75 (s, 3H), 2.55-2.20 (m, 2H), 1.46 (s, 3H), 1.41 (s, 6H).

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