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2-(S)-Hydroxymethyl-azetidine-1-carboxylic acid tert-butyl ester (prepared as described in Abreo, et al. J. Med. Chem. 1996, 39, 817-825) (9.7 g, 52 mmol) was taken up in dichloromethane (50 mL), treated with triethylamine (8.7 mL, 62 mmol), cooled to 0° C., treated dropwise with methanesulfonyl chloride (4.4 mL, 57 mmol), stirred overnight at ambient temperature, treated with sodium bicarbonate solution (50 mL) and the layers were separated. The aqueous layer was extracted with dichloromethane (50 mL). The combined organic layers were dried (MgSO4), filtered, concentrated and chromatographed on silica gel eluting with a gradient of 10:1, 5:1, 2:1 and 3:2 hexane:ethyl acetate to provide 10.7 g (78%). 1H NMR (300 MHz, CDCl3) δ 1.45 (s, 9 H) 2.27 (m, 2 H) 3.05 (s, 3 H) 3.82 (m, 2 H) 4.28 (dd, J=10.85, 2.71 Hz, 1 H) 4.43 (m, 1 H) 4.54 (dd, J=10.85, 4.07 Hz, 1 H).

1. customthe layers were separated
2. extractionThe aqueous layer was extracted with dichloromethane (50 mL)
3. dry with materialThe combined organic layers were dried (MgSO4)
4. filtrationfiltered
5. concentrationconcentrated
6. customchromatographed on silica gel eluting with a gradient of 10:1, 5:1, 2:1 and 3:2 hexane
7. customethyl acetate to provide 10.7 g (78%)