To a milky suspension of 5-chloro-3-fluoro-pyridine-2-carboxylic acid prepared in analogy of example 1b) (670 mg, 3.11 mmol, Eq: 1.00) in toluene (6 ml) at 25° C. was added DMF (11.4 mg, 12.0 μl, 155 μmol, Eq: 0.05). The mixture was cooled down to 0° C., then a solution of oxalyl chloride (434 mg, 299 μl, 3.42 mmol, Eq: 1.10) in toluene (2.00 ml) was dropped in within 10 min. The reaction mixture was stirred at 0° C. for 30 min, then without cooling for 3 h. At 0° C., (1S,4S)-2-oxa-5-aza-bicyclo[2.2.1]heptan-3-one methanesulfonate (CAS 769167-53-5) (650 mg, 3.11 mmol, Eq: 1.00) and THF (4.00 ml) were added to the reaction mixture, followed by TEA (1.18 g, 1.62 ml, 11.7 mmol, Eq: 3.75), dropped within 10 min (exothermic). The mixture was stirred at 22° C. for 16 h. The reaction mixture was poured into 20% aqueous citric acid solution (25 ml) and extracted with EtOAc (3×20 ml). The organic layers were dried over Na2SO4 and concentrated in vacuo. The crude material was purified by flash chromatography (silica gel, 40 g, 0% to 50% EtOAc in heptane) to yield the title compound as an orange oil (850 mg; 88%). m/z=311.1 [M+H]+.
