energy. The IR spectra were taken on a UR-20 spectrometer for KBr pellets, chloroform solution, or vaseline
mull. The thin-layer chromatography was carried out on Silufol UV-254 plates with detection by iodine vapor
and Ehrlich reagent. Preparative separation was carried out on a silica gel column (L5/40): 5 [Rf 0.52 (1:2
toluene–acetone)], 6a [Rf 0.62 (4:1 toluene–acetone)], 6b [Rf 0.75 (10:1 toluene–acetone)], 6c [Rf 0.52 (2:1
toluene–acetone)], 7 (Rf 0.67 (1:1 toluene–acetone)]. The chromatographic mobility, melting point, and NMR
spectral data of these compounds are identical to those found for authentic samples [2, 5-8].
2-(Ethoxycarbonyl)methyl-1-ethyl-2-hydroxy-4,6-dimethyl-1,2-dihydropyrimidine (2b). A solution
of salt 1b (2.1 g, 6 mmol) in absolute ethanol (7 ml) was cooled to 0°C and KOH (0.4 g, 6 mmol) pellets
(containing 85% KOH) in absolute ethanol (5 ml) was gradually added with stirring. The precipitate formed was
filtered off and washed with cold absolute ethanol (5 ml) to give 1.28 g (89%) pseudo base 2b. Mass spectrum,
m/z (Irel, %): 222 (67), 194 (15), 176 (69), 149 (100), 123 (68), 109 (10), 81 (18), 69 (28), 42 (36), 29 (21).
2-(Ethoxycarbonyl)methylidene-1,4,6-trimethyl-1,2-dihydropyrimidine (3a). A sample of pseudo
base 2a (1.13 g, 5 mmol) in CHCl3 (5 ml) was heated for 1 min. The solvent was distilled off and dried in
1
vacuum to give 1.02 g (98%) of anhydro base 3a. H NMR spectrum, δ, ppm (J, Hz): 1.28 (3H, t, J = 7.1,
CH3CH2O); 2.22 (3H, s, 4-CH3); 2.30 (3H, s, 6-CH3); 3.19 (3H, s, 1-CH3); 4.16 (2H, q, J = 7.1, OCH2CH3); 4.46
(1H, s, H-2'); 5.76 (1H, s, H-5). Mass spectrum, m/z (Irel, %): 208 (76), 179 (8), 162 (100), 136 (64), 134 (64),
108 (65), 93 (20), 80 (25), 65 (28), 55 (30), 43 (31), 28 (60).
2-(Ethoxycarbonyl)methylidene-1-ethyl-4,6-dimethyl-1,2-dihydropyrimidine (3b). By analogy to
the procedure for anhydro base 3a, pseudo base 2b (1.2 g, 5 mmol) gave 1.1 g (99%) of anhydro base 3b.
1H NMR spectrum, δ, ppm (J, Hz): 1.28 (3H, t, J = 7.1, CH3CH2O); 1.35 (3H, t, J = 7.1, CH3CH2N); 2.24 (3H, s,
4-CH3); 2.27 (3H, s, 6-CH3); 3.73 (2H, q, J = 7.1, N–CH2); 4.16 (2H, q, J = 7.1, OCH2); 4.54 (1H, s, H-2'); 5.71
(1H, s, H-5).
2-(Carbamoyl)methylidene-1,4,6-trimethyl-1,2-dihydropyrimidine (3c). A sample of KOH pellets
(containing 85% KOH) (0.33 g, 5 mmol) was dissolved in absolute ethanol (5 ml) and then added to a solution
of salt 1c (1.5 g, 4.9 mmol) in absolute ethanol (20 ml). The mixture was then heated for 1 min until the salt
completely dissolved. The solvent was distilled off in vacuum. The residue was washed with chloroform
(8 × 10 ml). Removal of the solvent gave 0.64 g (73%) anhydro base 3c. 1H NMR spectrum, δ, ppm (J, Hz): 2.18
(3H, s, 4-CH3); 2.20 (3H, s, 6-CH3); 3.14 (3H, s, 1-CH3); 4.49 (1H, s, H-2'); 5.23 (1H, br. s, NH); 5.62 (1H, s, H-
13
5); 8.87 (1H, br. s, NH). C NMR spectrum, δ, ppm: 21.11 (4-CH3), 24.76 (6-CH3), 34.62 (1-CH3), 84.39 (2-
CH), 103.14 (C(5)), 154.22 (C(4)), 154.74 (C(6)), 166.08 (C(2)), 171.39 (C=O). Mass spectrum, m/z (Irel, %): 179
(89), 162 (100), 149 (45), 135 (43), 108 (49), 94 (33), 67 (26), 55 (46), 42 (60), 28 (61).
Recyclization of Pseudo Base 2a upon Heating in Ethanol. A mixture of 2a (1.13 g, 5 mmol) in
absolute ethanol (10 ml) was heated for 10 h. The solvent was distilled off and the residue was washed with
chloroform. The chloroform extract was subjected to preparative separation by column chromatography using
2:1 toluene–acetone as the eluent to give 0.6 g (61%) pyridone 5, 0.07 g (7%) 6a, and 0.05 g (5%)
2-(ethoxycarbonyl)methyl-4,6-dimethylpyrimidine (7).
Recyclization of Pseudo Base 2a upon Reaction with Amines 4a-c in Ethanol (General Procedure).
A mixture of 2a (1.13 g, 5 mmol) and amine 4a-c (5 mmol) in absolute ethanol (10 ml) was heated at reflux for
12-16 h. The solvent and, in the case of methylamine, excess amine were distilled off. The residue was dissolved
in water and extracted with toluene (5 × 10 ml). Column chromatography of the toluene solution using 4:1
toluene–acetone as the eluent gave a) in the case of methylamine 4a, 0.48 g (49%) pyridone 5, 0.8 g (8%) 6a,
and 0.04 g (4%) 7, b) in the case of benzylamine 4b, 0.54 (55%) pyridone 5, 0.05 g (5%) 6a, 0.07 g (7%) 7, and
0.013 g (9%) 6b, and c) in the case of ethanolamine 4c, 0.58 g (60%) pyridone 5, 0.07 g (7%) 7, and 0.06 g (5%)
pyridine 6c.
Reaction of Salt 1a with Tris(hydroxymethyl)aminomethane (8) in Absolute Ethanol. A mixture of
salt 1a (4 g, 12 mmol) and amine 8 (4.35 g, 24 mmol) in absolute ethanol (15 ml) was heated at reflux for 30 h.
The precipitate formed was filtered off and recrystallized from absolute ethanol to give 0.78 g (32%)
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