Novel benzimidazole dilithium compound [1]

Full text of DOI:10.1007/s10593-006-0055-9

Chemistry of Heterocyclic Compounds, Vol. 42, No. 1, 2006
LETTERS TO THE EDITOR
NOVEL BENZIMIDAZOLE DILITHIUM COMPOUND
Yu. V. Koshchienko
Keywords: 1,5-dilithium benzimidazole, 5-chlorobenzimidazole, lithium naphthalene, metallation.
We have established that when 5-chlorobenzimidazole reacts with lithium naphthalene at -15°C in THF,
a novel benzimidazole dilithium compound is formed: 1,5-dilithium benzimidazole (1). The structure of
compound 1 was determined by converting it to (5-benzimidazolyl)diphenylcarbinol (2).
Arylhetarylcarbinols are formed when active organometallic compounds of N-substituted azoles are
reacted with aromatic aldehydes [1, 2]. However, when compound 1 is treated with aromatic aldehydes, instead
of the expected aryl(5-benzimidazolyl)carbinols, we obtained aryl (5-benzimidazolyl) ketones 3a,b.
OH
Ph2C
N
Ph2C=O
– +
Cl
Li
C10H8 Li
N
H
N
N
2
N
N
RC6H4CH=O
O
H
Li
1
N
R
N
H
3a,b
3 a R = H, b R = OMe
The 1H NMR spectra were taken on a Varian Unity 300 (300 MHz) in DMSO-d6, internal standard TMS.
The IR spectra were obtained on a Specord IR-75 spectrometer in nujol.
A solution of 5-chlorobenzimidazole (1.14 g, 7.5 mmol) in THF (10 ml) was added over a 5 min period,
with stirring under an argon atmosphere at -15°C, to lithium naphthalene obtained from finely ground lithium
(0.21 g, 30 mmol) and naphthalene (3.84 g, 30 mmol) in THF (20 ml). After 5 min, a solution of benzophenone
or an aromatic aldehyde (35 mmol) in THF (10 ml) was added. The mixture was held for 1 h at -15°C and then
for 2 h at 20-25°C, then a 20% aqueous solution of hydrochloric acid (15 ml) was added. The hydrochloric acid
layer was separated, washed twice with 15 ml ether each time, and treated with a 22% aqueous solution of
ammonia until pH > 7 was reached; the precipitate was filtered out, washed with water, and dried.
__________________________________________________________________________________________
Scientific Research Institute of Physical and Organic Chemistry, Rostov State University, Rostov-on-
Don 344090, Russia; e-mail: yukoshch@ipoc.rsu.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii,
No. 1, pp. 130-131, January, 2006. Original article submitted October 16, 2005.
0009-3122/06/4201-0115©2006 Springer Science+Business Media, Inc.
115

(5-Benzimidazolyl)diphenylcarbinol (2). Yield 32%; mp 194°C (alcohol). IR spectrum, ν, cm-1: 3210
(NH), 3400 (OH). 1H NMR spectrum, δ, ppm (J, Hz): 6.15 (1H, s, OH); 7.05 (1H, d, J = 8.5, H-6(7)); 7.16-7.26
(10H, m, C6H5); 7.33 (1H, s, H-4); 7.41 (1H, d, J = 8.5, H-7(6)); 7.95 (1H, s, H-2); 12.13 (1H, br. s, NH).
Found, %: C 79.89; H 5.45; N 9.43. C20H16N2O. Calculated, %: C 79.98; H 5.37; N 9.33.
5-Benzoylbenzimidazole (3a). Yield 37%; mp 124-125°C (alcohol). IR spectrum, ν, cm-1: 1650 (C=O),
1
2500-2800 (associated NH). H NMR spectrum, δ, ppm (J, Hz): 7.48-7.75 (7H, m, H-6,7, C6H5); 7.96 (1H, s,
H-4); 8.21 (1H, s, H-2); 12.58 (1H, br. s, NH). Found, %: C 75.53; H 4.64; N 12.65. C14H10N2O. Calculated, %:
C 75.66; H 4.54; N 12.60.
5-(p-Methoxybenzoyl)benzimidazole (3b). Yield 46%; mp 203-204°C (alcohol). IR spectrum, ν, cm-1:
1640 (C=O), 3200 (NH). 1H NMR spectrum, δ, ppm (J, Hz): 3.88 (3H, s, OCH3); 6.99 (2H, d, J = 8.5, H-3',5');
7.60 (2H, m, H-6,7); 7.75 (2H, d, J = 8.5, H-2',6'); 7.94 (1H, s, H-4); 8.20 (1H, s, H-2); 12.59 (1H, br. s, NH).
Found, %: C 71.31; H 4.87; N 11.19. C15H12N2O2. Calculated, %: C 71.42; H 4.79; N 11.10.
This work was carried out with the financial support of the Russian Foundation for Basic Research and
the Administration of Rostov Region (grant No. 04-03-96804).
REFERENCES
1.
2.
T. V. Talalaeva and K. A. Kocheshkov, Methods in Heteroorganic Chemistry. Lithium, Sodium,
Potassium, Rubidium, Cesium [in Russian], Nauka, Moscow (1971), Volume 2, p. 763.
B. A. Tertov and Yu. V. Koshchienko, Khim. Geterotsikl. Soedin., 147 (1988).
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