Chemistry of Heterocyclic Compounds 2016, 52(11), 948–951
filtered off and recrystallized from EtOH. The physico-
benzimidazole); 154.9 (C=O). Mass spectrum, m/z (Irel, %):
354 [M+H]+ (100). Found, %: C 71.44; H 4.32; N 19.77.
C21H15N5O. Calculated, %: C 71.38; H 4.28; N 19.82.
5-Methyl-4-[4-(5(6)-methyl-1H-benzimidazol-2-yl)-
phenyl]-2,4-dihydro-3H-1,2,4-triazol-3-one (5a). White
powder, mp 192–193°C. 1H NMR spectrum, δ, ppm
(J, Hz): 1.07 (3H, s, CH3); 2.47 (3H, s, CH3); 7.04 (1H, d,
J = 8.4, H Ar); 7.40 (1H, s, H Ar); 7.50 (1H, d, J = 8.4,
H Ar); 7.59 (2H, d, J = 8.8, H Ar); 8.26 (2H, d, J = 8.8,
H Ar); 11.68 (1H, s, NH); 12.79 (1H, s, NH). 13C NMR
spectrum, δ, ppm: 12.9 (CH3); 21.8 (CH3); 114.0; 115.2;
124.4; 127.7 (2C); 127.8 (2C); 129.5; 130.3; 132.2; 134.5;
144.1 (C=N triazole); 150.3 (C=N benzimidazole); 154.6
(C=O). Mass spectrum, m/z (Irel, %): 306 [M+H]+ (65).
Found, %: C 66.93; H 4.99; N 22.87. C17H15N5O. Calcu-
lated, %: C 66.87; H 4.95; N 22.94.
chemical properties of obtained compounds 3a–c were in
agreement with the published data.12
Synthesis of compounds 4–6. Microwave method A:
A mixture of the appropriate carboxylic acid 2 (10 mmol)
and the appropriate 1,2-diaminobenzene (10 mmol) in
concd H3PO4 (1.88 g, 1 ml, 20 mmol) was irradiated with
microwaves at 210°C (300 W maximum power) two times
for 2 min. After the completion of the reaction, the vial was
cooled to 60°C by air jet, and the resulting solution was
poured slowly into ice-cold water and neutralized to pH 5–6
with NaHCO3 solution. The precipitated product was
filtered off, washed with water, and recrystallized from
EtOH.
Microwave method B: A mixture of the appropriate
compound 1 (10 mmol) and compound 3 (10 mmol) in
DMF (1 ml) was irradiated in the microwave system at
165°C (200 W maximum power) for 6–7 min. After the
completion of the reaction (TLC control, EtOAc–hexane,
2:1), the purification according to the microwave method A
described above gave pure products 4–6.
5-Ethyl-4-[4-(5(6)-methyl-1H-benzimidazol-2-yl)phenyl]-
2,4-dihydro-3H-1,2,4-triazol-3-one (5b). White powder,
1
mp 191–192°C. H NMR spectrum, δ, ppm (J, Hz): 1.01
(3H, t, J = 7.6, CH3); 2.45 (3H, s, CH3); 2.51 (2H, q,
J = 7.6, CH2); 7.5 (1H, d, J = 8.0, H Ar); 7.36 (1H, s,
H Ar); 7.50 (1H, d, J =8, H Ar); 7.61 (2H, d, J = 8.4,
H Ar); 8.30 (2H, d, J = 8.4, H Ar); 11.75 (1H, s, NH);
12.88 (1H, s, NH). 13C NMR spectrum, δ, ppm: 10.1 (CH3);
19.8 (CH2); 21.8 (CH3); 114.0; 124.3; 127.7 (2C); 128.1
(2C); 128.4; 129.0; 130.6 (2C); 134.4; 148.2 (C=N
triazole); 150.4 (C=N benzimidazole); 154.8 (C=O). Mass
spectrum, m/z (Irel, %): 320 [M+H]+ (100). Found, %:
C 67.79; H 5.43; N 21.84. C18H17N5O. Calculated, %:
C 67.70; H 5.37; N 21.93.
Conventional method C: A mixture of the appropriate
acid 2 (10 mmol) and the corresponding 1,2-diamino-
benzene (10 mmol) in DMF (10 ml) was refluxed for 5–6 h
in an oil bath. After the completion of the reaction, the
mixture was poured into H2O and a solid precipitated. Pure
products 4–6 were isolated by using the same purification
methods as mentioned above (microwave method A).
4-[4-(1H-Benzimidazol-2-yl)phenyl]-5-methyl-2,4-di-
hydro-3H-1,2,4-triazol-3-one (4a). White powder, mp 234–
1
236°C. H NMR spectrum, δ, ppm (J, Hz): 2.12 (3H, s,
4-[4-(5(6)-Methyl-1H-benzimidazol-2-yl)phenyl]-5-phenyl-
2,4-dihydro-3H-1,2,4-triazol-3-one (5c). White powder,
CH3); 7.21–7.23 (2H, m, H Ar); 7.53–7.68 (4H, m, H Ar);
7.28 (2H, d, J = 8.0, H Ar); 11.69 (1H, s, NH); 13.01 (1H,
s, NH). 13C NMR spectrum, δ, ppm: 13.0 (CH3); 111.9;
119.5; 122.3; 123.3; 127.7; 127.9; 130.4; 134.6; 135.5;
144.3 (C=N triazole); 150.8 (C=N benzimidazole); 154.6
(C=O). Mass spectrum, m/z (Irel, %): 292 [M+H]+ (100).
Found, %: C 66.01; H 4.55; N 24.00. C16H13N5O.
Calculated, %: C 65.97; H 4.50; N 24.04.
1
mp 251–252°C. H NMR spectrum, δ, ppm (J, Hz): 2.42
(3H, s, CH3); 7.02 (1H, d, J = 8.0, H Ar); 7.31 (1H, s,
H Ar); 7.33–7.48 (8H, m, H Ar); 8.17 (2H, d, J = 8.4,
H Ar); 12.20 (1H, s, NH); 12.83 (1H, s, NH). 13C NMR
spectrum, δ, ppm: 21.8 (CH3); 124.4; 127.4; 127.6 (2C);
128.1 (2C); 128.5 (2C); 129.1 (2C); 130.4; 130.6; 132.2;
135.1; 145.7 (C=N triazole); 150.3 (C=N benzimidazole),
154.9 (C=O). Mass spectrum, m/z (Irel, %): 368 [M+H]+
(100). Found, %: C 72.00; H 4.71; N 18.99. C22H17N5O.
Calculated, %: C 71.92; H 4.66; N 19.06.
4-[(4-(1H-Benzimidazol-2-yl)phenyl]-5-ethyl-2,4-dihydro-
3H-1,2,4-triazol-3-one (4b). White crystals, mp 188–189°C.
1H NMR spectrum, δ, ppm (J, Hz): 1.12 (3H, t, J = 7.2,
CH3); 2.56 (2H, q, J = 7.2, CH2); 7.29–7.31 (2H, m, H Ar);
7.67–7.74 (4H, m, H Ar); 8.38–8.40 (2H, m, H Ar); 11.83
(1H, s, NH); 13.13 (1H, s, NH). 13C NMR spectrum, δ,
ppm: 10.2 (CH3); 20.0 (CH2); 112.1; 119.6; 122.5; 127.9;
128.3; 130.7; 134.7; 144.3; 148.3 (C=N triazole); 150.9
(C=N benzimidazole); 155.0 (C=O). Mass spectrum, m/z
(Irel, %): 306 [M+H]+ (100). Found, %: C 66.94; H 4.99;
N 22.88. C17H15N5O. Calculated, %: C 66.87; H 4.95;
N 22.94.
4-[4-(5,6-Dimethyl-1H-benzimidazol-2-yl)phenyl]-5-
methyl-2,4-dihydro-3H-1,2,4-triazol-3-one (6a). White
powder, mp 189–190°C. 1H NMR spectrum, δ, ppm (J, Hz):
2.11 (3H, s, CH3); 2.31 (6H, s, 2CH3); 7.36 (2H, s, H Ar);
7.55 (2H, d, J = 7.4, H Ar); 8.23 (2H, d, J = 7.4, H Ar);
11.67 (1H, s, NH); 12.72 (1H, s, NH). 13C NMR spectrum,
δ, ppm: 12.9 (CH3); 20.5 (2CH3); 114.1; 127.4 (3C); 127.8
(3C); 130.7; 134.2; 144.2 (C=N triazole); 149.9 (C=N
benzimidazole); 154.6 (C=O). Mass spectrum, m/z (Irel, %):
320 [M+H]+ (100). Found, %: C 67.79; H 5.43; N 21.87.
C18H17N5O. Calculated, %: C 67.70; H 5.37; N 21.93.
4-[4-(5,6-Dimethyl-1H-benzimidazol-2-yl)phenyl]-
5-ethyl-2,4-dihydro-3H-1,2,4-triazol-3-one (6b). White
powder, mp 330–331°C. 1H NMR spectrum, δ, ppm (J, Hz):
1.03 (3H, t, J = 6.8, CH3); 2.31 (6H, s, 2CH3); 2.47 (2H, q,
J = 6.8, CH2); 7.40 (2H, s, H Ar); 7.58 (2H, d, J = 7.2,
H Ar); 8.25 (2H, d, J = 7.2, H Ar); 11.70 (1H, s, NH);
4-[4-(1H-Benzimidazol-2-yl)phenyl]-5-phenyl-2,4-di-
hydro-3H-1,2,4-triazol-3-one (4c). White powder, mp 329–
1
330°C. H NMR spectrum, δ, ppm (J, Hz): 7.19–7.21 (2H,
m, H Ar); 7.38–7.47 (7H, m, H Ar); 7.59–7.61 (2H, m,
H Ar); 8.21 (2H, d, J = 6.0, H Ar); 12.20 (1H, s, NH);
13.11 (1H, br. s, NH). 13C NMR spectrum, δ, ppm: 122.8;
127.4 (2C); 127.7 (2C); 128.2 (2C); 128.6; 129.1 (2C);
130.4; 130.5; 135.2; 145.8 (C=N triazole); 150.7 (C=N
950