Pyridine → tert-butyl (5S)-5-methyl-1,2,3-oxathiazolidine-3-carboxylate 2-oxide

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Reaction Steps

A stirred solution of thionyl chloride (4.8 mL, 66.3 mmol) in acetonitrile (30 mL) is cooled down to −45° C. and a solution of tert-butyl [(2S)-2-hydroxypropyl]carbamate (5.1 g, 26.6 mmol) in acetonitrile (40 mL) is added by an addition funnel over 20 min, keeping the internal temperature below −40° C. DMAP (324 mg, 2.6 mmol) is added followed by the dropwise addition of pyridine (10.7 mL, 133.7 mmol), keeping the temperature below −40° C. The addition takes 1.5 h. Ethyl acetate (100 mL) is added to the suspension. The mixture is filtered at −35° C. to remove the solid and the solid is washed with EtOAc before it is discarded. Then the filtrates are combined, and sat. Na2HPO4 solution (40 mL) is added. Again the mixture is stirred vigorously for 30 min. Then the organic layer is separated, washed with 1M aqueous NaHSO4 to remove residual pyridine, dried (Na2SO4) and concentrated to afford a clear oil. The residue was taken up in diethyl ether, a small amount of insoluble material was removed and the filtrate was concentrated to afford the title compound (5.7 g, 97%) as an oil which was used in the next step without purification.

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