According to our ab initio (RHF/6-31G*) [9] calculations on the two tautomers, the phenyl and
pyrimidine rings are at 18° and 42° to each other in molecules 9 and 9A respectively. The experimentally
observed shift of the equilibrium towards structure 9 may be explained by its greater stability on account of
increased conjugation between the two rings.
EXPERIMENTAL
IR spectra of KBr disks were recorded with Bruker-25 instrument. 1H and 13C NMR spectra of DMSO-d6
solution were recorded with a Bruker DPX-400 instrument (400 and 100 MHz respectively).
N-amidinothiourea 2 was prepared according to [10].
[4-Phenyl-2H-1,3-thiazin]-2-ylideneguanidinium Perchlorate (3a). Benzoylacetylene 1 (0.65 g,
5 mmol) and HClO4 (58%, 0.58 ml) in glacial AcOH (10 ml) was added to a solution of N-amidinothiourea 2
(0.59 g, 5 mmol) in glacial AcOH (10 ml) and the mixture was stirred for 1 h at 20°C and kept for 24 h. The
precipitate was filtered off, washed with glacial AcOH (5 ml) and absolute ether until the smell of acetic acid
disappeared, and dried in vacuum to give compound 3a (1.19 g, 72%) as lemonish crystals; mp 165-167°C
(AcOH). IR spectrum, ν, cm-1: 3216-3379 (NH, N+H), 1658 (NH def.) 1534 -1576 (C=C, C=N), 1053-1120
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(ClO4 ). 1H NMR spectrum, δ, ppm (J, Hz): 7.57- 8.12 (5H, m, C6H5); 8.02 (1H, d, 3J = 5.30, C(6)H); 8.82 (1H, d,
3J = 5.30, C(5)H); 9.49 (2H, br. s, NH2); 10.00 (2H, br. s, N+H2). 13C NMR spectrum, δ, ppm; 116.25 (C(5));
127.69, 129.66, 132.63, 134.79 (C6H5); 159.68 (C(6)); 164.71 (C(4)); 165.00 (C(2)); 165.04 (Camidine). Found, %:
C 39.68; H 3.45; Cl 10.63; N 16.82; S 9.45. C11H10N4S·HClO4. Calculated, %: C 39.94; H 3.33; C 10.74;
N 16.94; S 9.68.
[4-Phenyl-2H-1,3-thiazin]-2-ylideneguanidinium Acetoxytrifluoroborate (3b) was obtained
analogously to compound 3a from compound 2 (0.59 g, 5 mmol), benzoylacetylene 1 (0.65 g, 5 mmol), and
BF3·Et2O (0.63 ml) in glacial AcOH (20 ml). Yield of compound 3b 1.2 g (67%), colorless crystals;
mp 145-146°C. IR spectrum, ν, cm-1: 3240-3370 (NH, N+H); 1660 (NH def.); 1534-1575 (C=C, C=N);
1
1000-1102 (B–F). H NMR spectrum, δ, ppm (J, Hz): 1.91 (3H, s, CH3); 7.61-8.16 (5H, m, C6H5); 7.96 (1H, d,
3J = 5.34, C(6)H); 8.86 (1H, d, 3J = 5.34, C(5)H); 9.51(2H, br. s, NH2); 9.98 (2H, br. s, N+H2). 13C NMR spectrum,
δ, ppm: 21.08 (CH3); 115.91 (C(5)); 127.44, 129.35, 132.30, 134.60 (C6H5); 159.50 (C(6)); 164.13 (C(4)); 164.73
(C(2)); 164.77 (Camidine). Found, %: C 43.30; H 3.58; F 15.55; N 15.83; S 8.79. C11H10N4S·CH3COOH·BF3.
Calculated, %: C 43.58; H 3.91; F 15.92; N 15.64; S 8.94.
N-Amidinothiourea Perchlorate (5). N-amidinothiourea 2 (3 g, 25 mmol) was heated in 58% HClO4
(30 ml) for 15 min, the solution was cooled, the precipitate was filtered off and washed with cold EtOH (5 ml)
and absolute ether and dried in vacuum to give colorless crystals of perchlorate 5 (5 g, 92%); mp 140-141°C. 13C
NMR spectrum, δ, ppm: 156.10 (C=N); 180.74 (C=S). Found, %: C 10.93; H 3.35; Cl 16.38; N 25.18; S 14.83.
C2H6N4S·HClO4. Calculated, %: C 10.99; H 3.23; Cl 16.22; N 25.63; S 14.67.
3-Amidino-2-benzoylvinylisothiourea Perchlorate (4a) and
[4-Phenyl-2H-1,3-thiazin]-2-
ylideneguanidinium Perchlorate (3a). A solution of benzoylacetylene 1 (0.65 g, 5 mmol) in AcOH (10 ml) was
added slowly to a suspension of the perchlorate of N-amidionthiourea 5 (1.09 g, 5 mmol) in glacial AcOH
(10 ml), the mixture was stirred for 2h, the precipitate was filtered off, washed with AcOH (5 ml) and absolute
ether, and dried in vacuum to give compound 4a (1.4 g, 80%) as a yellow powder; mp 148-150°C. IR spectrum,
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ν, cm-1: 3216-3411 (NH, N+H); 1642 (br, C=O, NH def.); 1538-1599 (C=C, C=N); 1060-1119 (ClO4 ). 1N NMR
spectrum, δ, ppm (J, Hz): 7.48 (1H, d, 3J = 9.68, cis-isomer, CαH); 8.15 (1H, d, 3J = 9.68, CβH); 7.59-8.07 (5H,
m, C6H5); 7.83 (2H, br. s, NH2); 8.25 (2H, br. s, NH2); 8.40 (2H, br. s, N+H2). 13C NMR spectrum, δ, ppm:
118.44 (Cα); 128.43, 129.24, 133.71, 136.80 (C6H5); 141.96 (Cβ); 161.28, 163.07 (2C, 2C=N); 189.10 (C=O).
Found, %: C 38.22; H 3.82; Cl 10.18; N 16.27; S 9.06. C11H12N4OS·HClO4. Calculated, %: C 37.88; H 3.73;
Cl 10.19; N 16.07; S 9.18.
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