TABLE 2. Parameters of the 1H NMR Spectra of Compounds Synthesized
Com-
pound
Chemical shifts, , ppm (J, Hz)
3a
3b
3.29 (3H, s, NCH3); 7.26-7.33 (8H, m, m-, p-H Ph, H-5,6); 7.39-7.41 (4H, m, o-H Ph);
7.51-7.54 (1H, m, H-7); 7.70-7.73 (1H, m, H-4); 13.88 (1H, s, NH)
3.29 (3H, s, NCH3); 3.69 and 3.72 (1.29H and 1.71H, two s, OCH3);
6.83 and 6.93 (0.82H and 1.18H, two d, J1 = J2 = 8.4, m-H Ar);
7.25-7.38 (9H, m, o-, m-, p-H Ph, o-H Ar, H-5,6); 7.51-7.54 (1H, m, H-7);
7.70-7.72 (1H, m, H-4); 13.72 and 13.75 (0.57H and 0.43H, two s, NH)
3c
3.31 (3H, s, NCH3); 7.26-7.38 (7H, m, H-5,6, o-, m-, p-H Ph); 7.54-7.56 (1H, m, H-7);
7.68-7.74 (3H, m, o-H Ar, H-4);
8.16 and 8.21-8.23 (1.50H and 0.50H, d, J = 8.1 and m, m-H Ar); 14.20 (1H, s, NН)
3d
3.33 (3H, s, NCH3); 7.27-7.38 (9H, m, H-5,6, o-, m-, p-H Ph, o-H Ar);
7.55-7.58 (1H, m, H-7); 7.73-7.75 (1H, m, H-4);
8.49, 8.55-8.57 (1.46H and 0.54H, d, J = 4.8 and m, m-H Ar);
14.18 and 14.26 (0.73H and 0.27H, two s, NН)
3e
3f
3.30 (3H, s, NCH3); 3.46 (6H, s, m-OCH3); 3.61 (3H, s, p-OCH3);
6.80 (2H, s, C6H2); 7.25-7.35 (5H, m, H-5,6, m-, p-H Ph); 7.46 (2H, d, J = 7.8, o-H Ph);
7.52-7.55 (1H, m, H-7); 7.71-7.74 (1H, m, H-4); 13.86 (1H, s, NН)
2.24, 3.26 (1.5H and 1.5H, two s, NCH3); 7.16-7.34 (2H, m, H-5,6);
7.31-7.45 (10H, m, H-7, o-, m-, p-H Ph, o-, m-, p-H Ar); 7.58-7.60 (1H, m, H-4);
13.79, 13.95 (0.50H and 0.50H, two s, NН)
TABLE 3. Content of Tautomer A in Benzimidazoles 3 and Their
Structural Analogs 1 and 2 in Equilibrium Mixture with Tautomer B from
1H NMR Spectral Data
Content of А, %
Ar
3
1
2 [14]
Ph (a)
А ≡ B
59
А ≡ B [12]
100 [13]
20 [12, 13]
21 [12]
—
А ≡ B
60
C6H4OMe-p (b)
C6H4NO2-p (c)
4-Pyridyl (d)
C6H2(OMe)3-m,m',p (e)
C6H4Cl-o (f)
25
—*
—*
—
27
—*
50
—
—
_______
* The 1H NMR spectrum does not distinguish between tautomers A and B.
group and this difference accounts for the lower rate of tautomeric interconversions such that each tautomer is
clearly seen in the spectrum.
Thus, 2-(3,5-diaryl-1H-pyrazol-4-yl)-1-methyl-1H-benzimidazoles are readily obtained in the cyclo-
condensation of 1-methyl-2-phenacyl-1H-benzimidazoles with aroylhydrazines. Introduction of a methyl group
at the nitrogen atom of the benzimidazole fragment does not alter the preferential stabilization for the tautomers
with electron-withdrawing aryl substituents at C-3 and electron-donor substituents at C-5 of the pyrazole ring
but reduces the difference between substituents at these positions.
EXPERIMENTAL
The 1H NMR spectra of these compounds were taken on a Varian VXR-300 spectrometer at 300 MHz in
DMSO-d6 with TMS as the internal standard. Monitoring of the course of the reactions and purity of the
products was carried out by thin-layer chromatography on Silufol UV-254 plates using benzene–ethanol, 9:1, as
the eluent and development with UV light.
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