and Tesla BS-567A spectrometers at 100 MHz with TMS or HMDS as the internal standards. Thin-layer
chromatography was carried out on Silufol UV-254 plates with development by iodine vapor, UV light,
KMnO4 + H2SO4 + H2O (0.5 g/2 ml/48 ml). The solvents were purified and dried by a standard procedure.
Ethyl Esters of 4,5-Disubstituted 2-Amino-3-thiophenecarboxylic Acids were prepared by
cyclization of ethyl cyanoacetate with sulfur and the corresponding ketone (methyl ethyl ketone or
cyclohexanone) [6, 7].
5,7-Dimethyl-2-tioxopyrido[2,3-d]pyrimidin-4-one (4) was obtained by a variant of the method of
Khodzhanizov [8]. Acetylacetone (0.84 ml, 8 mmol) was added to
a
suspension of 6-amino-
2-thioxo-4-pyrimidinone (1 g, 7 mmol) [8] in trifluoroacetic acid (2.8 ml). The mixture was heated on a water
bath for 2.5 h and cooled. Water was added and the precipitate formed was filtered off, dried, and recrystallized
from benzene to give 1.3 g (90%) 4, mp 292°C, Rf 0.57 (8:1 chloroform–methanol). IR spectrum, ν, cm-1: 1680
(νC=O), 3080, 3150 (νNH). Mass spectrum, m/z (Irel, %): 207 [M]+ (100), 179 [M–CO]+ (6), 174 [M-SH]+ (14),
1
148 [M–HNCS]+ (19), 121 [M–CO–NCS]+ (13). H NMR spectrum, δ, ppm: 2.35 (3H, s, 5-CH3); 2.58 (3H, s,
7-CH3); 7.30 (1H, s, H-6).
5,6-Dimethyl-2-thioxothieno[2,3-d]pyrimidin-4-one (5a) was obtained by a modification of the
method of Shodiev [9] from the ethyl ester of 2-amino-3-thiophenecarboxylic acid and ammonium thiocyanate
(instead of potassium thiocyanate). A suspension of ethyl ester of 2-amino-3-thiophenecarboxylic acid (20 g,
0.1 mol), ammonium thiocyanate (7.6 g, 0.1 mol), and o-xylene (50 ml) was heated with stirring on a water bath.
Concentrated hydrochloric acid (15 ml, 0.1 mol) was added dropwise over 30 min. Heating was continued at this
temperature for an additional 6 h. After cooling, the precipitate formed was filtered off, washed with water, and
dried. The precipitate was dissolved in 10% aqueous potassium hydroxide. The insoluble fraction was filtered
off. The mother liquor was neutralized by adding acetic acid. The precipitate formed was separated, washed with
water, and dried to give 15.5 g (73%) 5a, mp 313-315°C (acetone), Rf 0.45 (1:3 acetone–benzene). IR spectrum,
ν, cm-1: 1670 (νC=O), 3410 (νNH). Mass spectrum, m/z (Irel., %): 212 [M]+ (100), 179 [M–SH]+ (15), 153 [M–
HNCS]+ (60). 1H NMR spectrum, δ, ppm: 2.00 (6H, s, 5-CH3, 6-CH3).
5,6-Tetramethylene-2-thioxothieno[2,3-d]pyrimidin-4-one (5b) was obtained according to Shodiev [9]
in 35% yield (8 g), mp 288-289°C (mp 287-289°C [9]), Rf 0.5 (1:3 acetone–benzene). Mass spectrum, m/z (Irel, %):
238 [M]+ (100), 210 [M–CO]+ (20), 179 [M–HNCS]+ (70), 151 [M–CO–HNCS]+ (54). 1H NMR spectrum, δ, ppm
(J, Hz) in pyridine-d5: 0.80 (2H, d, J = 8, H-5); 1.00-1.70 (4H, m, H-6, H-7); 2.40 (d, J = 7, H-8).
2,3,9,10-Tetramethyl-4H,11H-[1,2,4]thiadiazolo[3,2-b:5,4-b']bis(thieno[2,3-d]pyrimidine-4,11-dione)
(7). A. Iodine (0.25 g, 1.5 mmol) was added to a solution of 5,6-dimethyl-2-thioxothieno-[2,3-d]pyridimidin-
4-one (212 mg, 1 mmol) in absolute methanol (3 ml), heated at reflux for 15 min, and then cooled. Water was
added. The aqueous solution was heated at reflux and cooled. The precipitate formed was filtered off, washed
with water, recrystallized from DMF and dried to give 117 mg (61%) 7, mp 245-247°C, Rf 0.90 (3:2 benzene–
acetone). IR spectrum, ν, cm-1: 1675-1680 (νC=O). Mass spectrum, m/z (Irel, %): 388 [M]+ (100), 360 [M–CO]+
(20), 330 [M–NCS]+ (30), 316 [M–SNCO]+ (65). Found, %: C 49.30; H 3.10; N 14.33. C16H12N4O2S3.
Calculated, %: C 49.47; H 3.11; N 14.42.
B. P2O5 (200 mg, 1.4 mmol) was added to a solution of 5,6-dimethyl-2-thioxothieno[2,3-d]pyrimidin-
4-one (212 mg, 1 mmol) in DMSO (10 ml) and stirred at room temperature for 4 h. Water was added and the
precipitate formed was filtered off, washed with water, DMF, and ether, and dried at room temperature to give
134 mg (70%) 7, mp 245-247°C, Rf 0.90 (3:2 benzene–acetone).
1,2,3,4,10,11,12,13-Octahydro[1,2,4]thiadiazolo[3,2-b:5,4b']bis(benzo[b]thiophene[2,3-d]-pyrimidine-
5,14-dione) (8). A. By analogy to the above procedure, 5,6-tetramethylene-2-thioxothieno[2,3-d]pyrimidin-4-one
(240 mg, 1 mmol) yielded 154 mg (70%) 8, mp 262-264°C, Rf 0.53 (2:3 acetone–benzene). IR spectrum, ν, cm-1:
1665-1670 (νC=O). Mass spectrum, m/z (Irel, %): 440 [M]+ (100), 412 [M–CO]+ (15), 382 [M-NCS]+ (15), 362
[M–SNCO]+ (19). Found,%: C 54.40; H 3.52; N 12.51. C20H16N4O2S3. Calculated, %: C 54.53; H 3.66; N 12.72.
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