Cl.N[C:3]1[C:4]([O:13][CH3:14])=[N:5][CH:6]=[C:7]([CH:12]=1)[C:8]([O:10][CH3:11])=[O:9].N([O-])=[O:16].[Na+].F[B-](F)(F)F.[Na+]>O>[OH:16][C:3]1[C:4]([O:13][CH3:14])=[N:5][CH:6]=[C:7]([CH:12]=1)[C:8]([O:10][CH3:11])=[O:9]Concentrated hydrochloric acid (9.06 mL of strength 36%) is added to a stirred suspension of methyl 5-amino-6-methoxynicotinoate (3.3 g) in water (20 mL). The mixture is cooled to 0° C. and treated dropwise with a solution of sodium nitrite (1.37 g) in water (5 mL). After 30 minutes at 0° C. a solution of sodium tetrafluoroborate (2.84 g) in water (10 mL) is added. After a further 30 minutes the precipitated diazonium salt is collected, washed with a little ice-cold water then with diethyl ether and sucked dry. Potassium carbonate (1.0 g) is added to trifluoroacetic acid (32 mL) at 0° C. followed by the addition of the diazonium salt in one portion. The mixture is stirred at reflux for 18 hours, cooled then poured into iced water and stirred for 1 hour. The aqueous mixture is neutralised with solid sodium bicarbonate and extracted with ethyl acetate. The extracts are washed with water and dried (MgSO4). Concentration afforded methyl 5-hydroxy-6-methoxynicotinoate (2.86 g) as a beige solid. This material is used without further purification.
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