[NH2:1]/[C:2](/[CH3:8])=[CH:3]\[C:4]([O:6][CH3:7])=[O:5].O[C:10](=[C:13]1C(=O)OC(C)(C)[O:15][C:14]1=O)[CH2:11][CH3:12].CCOCC>CCCCCC>[CH2:11]([C:10]1[NH:1][C:2]([CH3:8])=[C:3]([C:4]([O:6][CH3:7])=[O:5])[C:14](=[O:15])[CH:13]=1)[CH3:12]A mixture of methyl 3-aminocrotonate (5 g) and 5-(1-hydroxypropylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione (10 g) (obtained as described in J. Org. Chem., 1978, 43, 2087) was heated at 120° C. for 1 hour. The residue was cooled to ambient temperature and treated with a mixture of ether and hexane (1:6 v/v; 35 ml) and allowed to stand for 18 hours. The solvent was removed by decanting and the insoluble residue purified by flash chromatography, eluting with methanol/dichloromethane (1:9 v/v) to give methyl 1,4-dihydro-6-ethyl-2-methyl-4-oxopyridine-3-carboxylate (1 g), as a yellow solid, m.p. 176°-180° C.; NMR (CDCl3): 1.2(t,3H); 2.45(s,3H), 2.45(q,2H), 3.8(s,3H), 6.3(s,1H); mass spectrum (chemical ionisation, ammonia): 196(M+H)+.
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