Trifluoromethanesulfonic anhydride → Methyl 3-(trifluoromethylsulfonyloxy)-pyridine-2-carboxylate

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Triflic anhydride (5.0 g, 18.0 mmol) was added dropwise to a cold (0° C.) solution of methyl 3-hydroxypicolinate (2.5 g, 16.3 mmol) and TEA (2.5 mL, 18.0 mmol) in CH2Cl2 (80 mL). The mixture was stirred at 0° C. for 1 h before it was allowed to warm up to room temperature where it stirred for an additional 1 h. The mixture was then quenched with saturated NaHCO3 solution (40 mL) and the organic layer was separated, washed with brine, dried over MgSO4 and concentrated to give methyl 3-(trifluoromethylsulfonyloxy)picolinate (i.e. Cap-174, step a) (3.38 g, 73%) as a dark brown oil (>95% pure) which was used directly without further purification. 1H NMR (300 MHz, CDCl3) δ ppm 8.72-8.79 (1H, m), 7.71 (1H, d, J=1.5 Hz), 7.58-7.65 (1H, m), 4.04 (3H, s). Rt=1.93 min (Cond.-MD1); LC/MS: Anal. Calcd. for [M+H]+ C8H7F3NO5S: 286.00. found: 286.08.

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