[CH:1]([O:8][CH2:9][CH3:10])([O:5]CC)OCC.C(OC(=O)C)(=O)C.C([O:20][C:21](=O)[CH:22]([CH3:31])[C:23](=[O:30])[CH2:24][C:25](OCC)=O)C.[CH3:33][NH2:34]>C(OCC)C.O>[CH2:9]([O:8][C:1]([C:24]1[C:23]([OH:30])=[C:22]([CH3:31])[C:21](=[O:20])[N:34]([CH3:33])[CH:25]=1)=[O:5])[CH3:10]
Triethyl orthoformate (3.85 mL, 23.12 mmol) and acetic anhydride (4.37 mL, 46.25 mmol) were added to 2-methyl-3-oxo-pentanedioic acid diethyl ester (Caliskan et al Aust. J. Chem. 1999, 52 (11), 1013-1020) (5.0 g, 23.1 mmol) and the reaction mixture heated to 135° C. After 1 hour, the reaction mixture was cooled to room temperature and concentrated under reduced pressure. The residue was cooled to 0° C. and methylamine (40% in water, 5.0 mL, 57.81 mmol) was added with stirring. Water (20 mL) was added and the reaction mixture stirred for 16 hours. The reaction mixture was extracted with ethyl acetate and the aqueous layer acidified to pH 2 with 10% aqueous HCl. The acidified aqueous layer was extracted with ethyl acetate. The combined organic extracts were dried (MgSO4) and concentrated to give a solid. Trituration with diethyl ether yielded 4.88 g (55%) clean desired product. 4-Hydroxy-1,5-dimethyl-6-oxo-1,6-dihydropyridine-3-carboxylic acid ethyl ester was carried forward as described in Example 1, Steps B-D. MS APCI (−) m/z 353, 355 (M−, Br pattern) detected; 1H NMR (400 MHz, CD3OD) δ 8.49 (s, 1H), 7.36 (dd, 1H), 7.24 (dd, 1H), 6.71 (m, 1H), 3.60 (s, 3H), 1.68 (s, 3H).
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