4-Toluenesulfonyl chloride → tert-Butyl 3-(tosyloxy)pyrrolidine-1-carboxylate

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To a solution of N-tert-butoxycarbonylpyrrolidin-3-ol (19.8 g, 0.106 mol) in pyridine (200 ml) at 0° C. under nitrogen was added tosyl chloride (22.3 g, 0.117 mol) portionwise. Stir at 0° C. for 2 hr, warm to room temperature and stir at room temperature overnight. The pyridine was evaporated in vacuo and the residue was partioned between EtOAc and saturated aqueous citric acid (200 ml each). The aqueous layer was extracted with EtOAc (2×200 ml) and the combined organics were dried (sodium sulphate), filtered and evaporated to leave an oil which was purified by flash silica gel column chromatography using 10% EtOAc/cyclohexane as eluent to give in F40-85 an oil. The oil was dissolved in a small volume of cyclohexane/diethylether (5:1, 50 ml), cooled and scratched with a spatula to induce crystallisation. The resulting solid was filtered to give tert-butyl 3-[(4-methylphenyl)sulfonyl]oxy-1-pyrrolidinecarboxylate (10.5 g, 29%) as a white solid. Rf in EtOAc/cyclohexane=0.13. 1H NMR (CDCl3, 250 MHz): 7.79 (2H, d), 7.35 (2H, d), 5.04 (1H, m), 3.43 (4H, m), 2.46 (3H, s), 2.03-2.20 (2H, bm), 1.43 (9H, s).

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