Dimethylformamide → 2,3-Dichloroisonicotinaldehyde

To a solution of 2,3-dichloropyridine [C.A.S. 2402-77-9] (10 g, 67.57 mmol) in dry THF (200 ml) cooled at −78° C. under a nitrogen atmosphere, was added dropwise n-butyllithium (37.165 ml, 74 mmol, 2 M in hexanes). The resulting reaction mixture was stirred at −78° C. for 20 min. Then dry DMF (6.28 ml, 81.087 mmol) was added dropwise. After 15 min. stirring at −78° C., the mixture was allowed to warm to r.t., quenched with water and extracted with DCM. The combined organic extracts were dried (Na2SO4) and concentrated in vacuo. The crude residue was purified by short open column chromatography (DCM as eluent). The desired product fractions were collected and concentrated in vacuo to give a residue that was further purified by column chromatography (silica gel; DCM/heptane up to 50% as eluent). The desired fractions were collected and concentrated in vacuo to yield intermediate compound D36 (4.15 g, 34.9%) as a white solid.