NH), 8.05 (1H, s, H-6); 2.42 (3H, s, CH3). 13C NMR spectrum, , ppm: 194.4 (CO); 163.1 (C-4); 151.5, 149.4
(C-6 + C-2); 111.9 (C-5); 30.9 (CH3). Mass spectrum, m/z (Irel, %): 155 (7), 154 [M]+ (76), 139 (100), 91 (29),
69 (51).
Hydrolysis of Ethyl 4-Methyl-2-oxo-1H-pyrimidine-5-carboxylate (1b). Ester 1b (1.5 g, 8.3 mmol)
was added to a solution of potassium hydroxide (10%, 33 ml) and refluxed for 1 h. Conc. HCl (8 ml) was added.
Water was evaporated and the residue was dried in air to give a mixture of 4-methyl-2-oxo-1H-pyrimi-dine-5-
carboxylic acid (3b) and potassium chloride (5.2 g). 1H NMR spectrum, , ppm: 8.85 (1H, s, H-6); 2.62 (3H, s,
CH3). 13C NMR spectrum, , ppm: 172.8 (CO); 164.6 (C-6); 160.9 (C-4); 151.3 (C-2); 108.5 (C-5), 21.5 (CH3).
Attempts to prepare acid 3b in a pure state led to its decomposition, the only identified product being the 4-
methylpyrimidin-2-one (6) formed via decarboxylation. Its formation was judged from the following signals in
the 1H NMR spectrum, , ppm (J, Hz): 8.61 (1H, d, J = 6.3, H-6); 6.85 (1H, d, J = 6.3, H-5).
Ethyl 4-Methyl-2-thioxo-1H-pyrimidine-5-carboxylate (1c) and 5-Acetylthiouracil (2c). Thiourea
(7.6 g, 100 mmol) was added to a solution of sodium ethylate (sodium (2.3 g, 100 mmol) in absolute ethanol
(150 ml)). Following solution, ethoxymethyleneacetoacetate (18.6 g, 100 mmol) was added portionwise and the
product was refluxed with stirring for 8 h.
The sodium salt of ketone 2c was insoluble in sodium ethylate solution and was filtered off and
dissolved in water. The solution was acidified with acetic acid and the precipitated ketone was filtered off. The
ketone 2c was recrystallized from alcohol to give 5-acetylthiouracil (2c) (5.15 g, 30%); mp 270-271ºC. 1H NMR
spectrum, , ppm: 12.82 (2H, s, NH); 7.88 (1H, s, H-6); 2.44 (3H, s, CH3). 13C NMR spectrum, , ppm: 194.4
(CO); 177.3 (C-2); 160.2 (C-4); 147.0 (C-6); 115.4 (C-5); 31.1 (CH3). Mass spectrum, m/z (Irel, %): 172 (6), 171
(9), 170 [M]+ (100), 155 (35), 96 (12), 87 (8), 83 (15). Found, %: C 42.35, 42.31; H 3.71; 3.73; N 16.18, 16.21.
C6H6N2O2S. Calculated, %: C 42.34; H 3.55; N 16.46.
The filtrate after separation of the salt of ketone 2c was evaporated to dryness. The sodium salt of ester
1c was dissolved in water and acidified with acetic acid. The precipitate was filtered off and recrystallized from
1
alcohol to give ester 1c (10.4 g, 53%); mp 186-187ºC (mp 188-189ºC [5]). H NMR spectrum, , ppm (J, Hz):
14.05 (1H, s, NH); 8.56 (1H, s, H-6); 4.26 (2H, q, J = 7.0, OCH2CH3); 2.58 (3H, s, CH3); 1.29 (3H, t, J = 7.0,
OCH2CH3). 13C NMR spectrum, , ppm: 182.9 (C-2); 165.5 (CO); 163.5 (C-6); 156.4 (C-4); 111.7 (C-5); 61.1
(OCH2CH3); 21.3 (CH3); 14.3 (OCH2CH3). Mass spectrum, m/z (Irel, %): 200 (6), 199 (11), 198 [M]+ (100), 153
(44), 112 (28), 68 (31).
Hydrolysis of Ethyl 4-Methyl-2-thioxo-1H-pyrimidine-5-carboxylate (1c). Ester 1c (2 g, 10 mmol)
was added to potassium hydroxide solution (10%, 40 ml) and refluxed for 10 min. Conc. HCl (10 ml) was
added, the product was cooled, and the precipitated solid was filtered off to give a mixture of compounds which
we were unable to separate or identify.
Ethyl 4-Amino-2-thioxo-1H-pyrimidine-5-carboxylate (1d). Thiourea (15 g, 200 mmol) was added to
a solution of sodium ethylate (sodium (4.6 g, 200 mmol) in absolute ethanol (125 ml)). The solution obtained
was stirred and ethyl ethoxymethylenecyanoacetate (33.8 g, 200 mmol) was added portionwise and refluxed for
6 h. The cooled product was treated with water (350 ml), acidified with acetic acid (30 ml), and taken to reflux
with stirring. The solution was cooled and the precipitate formed was filtered off, washed with water, and dried.
Yield 27.8 g (76%); mp 258-259ºC (mp 260-262ºC [11]). 1H NMR spectrum, , ppm (J, Hz): 12.46 (1H, s, NH);
8.48, 7.87 (2H, s, NH2); 8.05 (1H, s, H-6); 4.23 (2H, q, J = 7.0, OCH2CH3); 1.27 (3H, t, J = 7.0; OCH2CH3). 13C
NMR spectrum, , ppm: 181.2 (C-2); 165.2 (CO); 160.4 (C-4); 148.7 (C-6); 97.6 (C-5); 61.7 (OCH2CH3); 14.9
(OCH2CH3). Mass spectrum, m/z (Irel, %): 201 (6), 200 (10), 199 [M]+ (100), 171 (9), 154 (9), 141 (10), 127
(13), 113 (28), 95 (38), 68 (22).
Hydrolysis of Ethyl 4-Amino-2-thioxo-1H-pyrimidine-5-carboxylate (1d). A mixture of aqueous
potassium hydroxide (10%, 100 ml) and ester 1d (4.58 g, 25 mmol) was refluxed for 10 min. Hydrochloric acid
(25 ml) was added and the precipitated solid was filtered off, washed with water, and dried. Yield of compound
3d 3.08 g (80%). Decomposition point 261-262ºC (decomposition point 253-263ºC [12]). 1H NMR spectrum, ,
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