CS(C)=O.C(Cl)(=O)C(Cl)=O.[Br:11][C:12]1[C:17]([CH3:18])=[CH:16][N:15]=[C:14]([CH2:19][OH:20])[CH:13]=1.C(N(CC)CC)C>C(Cl)Cl.O>[Br:11][C:12]1[C:17]([CH3:18])=[CH:16][N:15]=[C:14]([CH:19]=[O:20])[CH:13]=1A solution of dimethyl sulfoxide (0.85 mL, 12.02 mmol) in DCM (10 mL) was added dropwise over 5 minutes to a solution of oxalyl chloride (0.47 mL, 5.51 mmol) in DCM (20 mL) at −78° C. under an atmosphere of N2 (gas evolved). Stirring was continued for 10 minutes. To this solution was added (4-bromo-5-methyl-2-pyridyl)methanol [CAS: 820224-83-7](1.01 g, 5.01 mmol) in DCM (2 mL) dropwise over a period of 10 minutes. Stirring was then continued for a further 10 minutes. Triethylamine (3.13 mL, 22.54 mmol) was added dropwise and stirring continued for 5 minutes, before allowing the reaction to warm to room temperature. Water was added and the phases were separated by passing over a hydrophobic frit. The organic phase was evaporated to yield a dark brown solid which was dried under vacuum overnight (795 mg). This was purified by column chromatography on silica gel (0-100% EtOAc in isohexane) to yield 4-bromo-5-methyl-pyridine-2-carbaldehyde (D21) (619 mg, 3.0945 mmol, 61.8% yield) as an orange crystalline solid;
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