Reaction of 2-(1-aryl-5-phenylpyrazol-4-yl)-1H-benzimidazoles with the dimethylacetal of DMF [5]

Full text of DOI:10.1007/s10593-007-0078-x

Chemistry of Heterocyclic Compounds, Vol. 43, No. 4, 2007
REACTION OF 2-(1-ARYL-5-PHENYLPYRAZOL-4-YL)-1H-
BENZIMIDAZOLES WITH THE DIMETHYLACETAL OF DMF
I. B. Dzvinchuk and M. O. Lozinskii
Keywords: dimethyl acetal of DMF, 2-(4-pyrazolyl)benzimidazoles, N-methylation.
Previously [1] we assigned the structure 2a,b to the products of the reaction of 2-(1-aryl-
5-phenylpyrazol-4-yl)-1H-benzimidzoles 1a,b with the dimethylacetal of DMF. This conclusion did not
1
contradict the H NMR spectral data, the elemental analysis, and information [2] on the existence of
polycondensation of heterocyclic systems of this type. The result appeared to be unusual on the background of
known [3-5] properties of the dimethylacetal of DMF.
Ph
N
N
N
Ar
Ph
Ar
N
N
N
N
H
Me2NCH(OMe)2
OMe
N
2a,b
Ph
H
Ar
N
N
N
1a,b
N
– MeOH,
– HCONMe2
Me
3a,b
1–3 a Ar = Ph, b Ar = 4-O2NC6H4
Over time, we had doubts about the correctness or our conclusions. We carried out additional chromato-
mass–spectroscopic analysis and detected that the molecular mass did not coincide with that calculated for the
structure 2a,b. A second elemental analysis was carried out after thorough purification of the products. As a
result it became evident that our original suggestion of the structure of the products was erroneous. In particular
in the reaction cyclocondensation does not take place, but N-methylation at the benzimidazole nitrogen atom
with formation of the compounds 3a,b, which accords with the known properties of the dimethylacetal of DMF
[5].
1H NMR spectra of DMSO-d6 solutions with TMS as the internal standard were recorded on a Varian
VXR-300 (300 MHz) instrument. Chromatomass spectrometry was carried out on an Agilent 1100 series high
resolution liquid chromatograph equipped with an Agilent LC MSD SI ( Parameters: Zorbax SB-C18 column,
1.8 µm, 4.6 mm, 15 mm, solvent acetonitrile–water (95:5), 0.1% trifluoroacetic acid, rate of elution 3ml/s; 1 µl
sample injected; chemical ionization at atmospheric pressure with simultaneous scans of positive an negative
ions with masse from 80-1000 m/z).
__________________________________________________________________________________________
Institute of Organic Chemistry, Ukraine National Academy of Sciences, Kiev 02094; e-mail:
Rostov@bcpi.kiev.ua. Translated from Khimiya Geterotsiklicheskikh Soedienii, No. 4, 618-619, April, 2007.
Original article submitted November 17, 2006.
0009-3122/07/4304-0513©2007 Springer Science+Business Media, Inc.
513

Compounds 3a,b were prepared by method [1] and were dried in a vacuum of a water pump at 115°C
for 5 h before elemental analysis.
1-Methyl-2-[1,5-diphenylpyrazol-4-yl)-1H-benzimidazole (3a). Yield 88%; mp 190-191.5°C.
1H NMR spectrum, δ, ppm: 3.43 (3H, s, CH3-1); 7.18-7.42 (12H, m, H-5,6 + CC6H5 + NC6H5); 7.47-7.50 (1H,
m, H-7); 7.60-7.63 (1H, m, H-4); 8.10 (1H, s, H-3'). Chromatomass–spectrometric analysis: purity > 99%.
Found: M + 1 = 351. Calculated: M = 350. Found, %: C 78.48; H 5.02; N 15.52. C23H18N4. Calculated, %:
C 78.83; H 5.18; N 15.99.
1-Methyl-2-[1-(4-nitrophenyl)-5-phenylpyrazol-4-yl]-1H-benzimidazole (3b). Yield 89%; mp
1
202-207.5°. H NMR spectrum, δ, ppm (J, Hz): 3.46 (3H, s, CH3-1); 7.19-7.43 (7H, H-5,6 + C6H5); 7.49-7.52
(1H, m, H-7); 7.57 and 7.28 (2 + 2H, two d, J = 9, C6H4NO2); 7.61-7.64 (1H, m, H-4); 8.34 (1H, s, H-3').
Chromatomass–spectrometric analysis: Purity > 99%. Found: M+1 =396. Calculate: M = 395. Found, %:
C 69.58; H 4.15; N 17.45. C25H18N4. Calculated, %: C 69.86; H 4.33; N 17.71.
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