Received 5 July 2005
aGrupo de Investigación de Compuestos Heterocíclicos, Departamento de Química, Universidad de Valle, AA 25360 Cali, Colombia,bDepartamento de Química Inorgánica y Orgánica, Universidad de Jaén, 23071 Jaén, Spain,cDepartment of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, Scotland, and dSchool of Chemistry, University of St Andrews, St Andrews, Fife KY16 9ST, Scotland
Correspondence e-mail: email@example.com
Molecules of the title compound, C22H20N4O2, are linked by paired C-HO hydrogen bonds into centrosymmetric R22(18) dimers and these dimers are linked into chains by paired C-H(arene) hydrogen bonds.
We have recently described the preparation of pyrazolo[3,4-b]pyridines from 5-aminopyrazoles in solution with different reactants (Low et al., 2002, and references therein), and we have reported the crystal structure of the fully aromatized 3-methyl-1,4-diphenyl-1H-pyrazolo[3,4-b]pyridine (Low et al., 2002). We report here an analogous structure, that of 3-tert-butyl-4-(4-nitrophenyl)-1-phenyl-1H-pyrazolo[3,4-b]pyridine, (I), obtained from the solvent-free reaction of the corresponding 5-aminopyrazole and the Mannich adduct -dimethylamino-4-nitropropiophenone hydrochloride, under microwave irradiation. The title compound, (I), was obtained along with the reduced 6-(4-nitrophenyl) analogue, (II); however, in pyridine solution under reflux, a similar reaction yielded regioselectively the isomeric 6-arylpyrazolo[3,4-b]pyridine (Quiroga et al., 1998).
Neither of the aryl rings in compound (I) (Fig. 1) is coplanar with the pyrazolopyridine system; unsubstituted phenyl ring C11-C16 makes a dihedral angle of 25.3 (2)° with the adjacent pyrazole ring, while substituted ring C41-C46 is nearly orthogonal to the pyridine ring, with a dihedral angle between these ring planes of 85.1 (2)°; in addition, the nitro group makes a dihedral angle of 11.6 (2)° with the adjacent aryl ring. The bond distances within the fused heterocyclic ring system (Table 1) are consistent with electronic delocalization in the pyridine ring and strong bond fixation in the pyrazole ring.
The molecules of compound (I) are linked into chains of fused rings by a combination of one C-HO hydrogen bond and one C-H(arene) hydrogen bond (Table 2). Pyridine atom C5 in the molecule at (x, y, z) acts as hydrogen-bond donor to nitro atom O41 in the molecule at (1 - x, 1 - y, 1 - z), generating a centrosymmetric R22(18) dimer centred at (, , ) (Fig. 2). In addition, aryl atoms C43 in the molecules at (x, y, z) and (1 - x, 1 - y, 1 - z), which are both components of the R22(18) dimer centred at (, , ), act as donors respectively to aryl rings C11-C16 in the molecules at (-x, 1 - y, -z) and (1 + x, y, 1 + z), which themselves are components of the R22(18) dimers centred at (-, , -) and (, , ). Propagation by inversion of these two interactions thus generates a chain of edge-fused rings running parallel to the  direction, rings built from paired C-HO hydrogen bonds centred at (n + , , n + ) (n = zero or integer) and rings built from paired C-H(arene) hydrogen bonds centred at (n, , n) (n = zero or integer) (Fig. 3).
| || Figure 1 |
The molecule of compound (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
| || Figure 2 |
Part of the crystal structure of (I), showing the formation of a centrosymmetric R22(18) dimer. For the sake of clarity, the H atoms not involved in the motif shown have been omitted. Atoms marked with an asterisk (*) are at the symmetry position (1 - x, 1 - y, 1 - z). Dashed lines indicate hydrogen bonds.
| || Figure 3 |
Stereoview of part of the crystal structure of (I), showing the formation of a  chain of edge-fused rings. For the sake of clarity, the H atoms not involved in the motifs shown have been omitted. Dashed lines indicate hydrogen bonds.
Equimolar quantities (0.465 mmol) of 5-amino-3-tert-butyl-1-phenyl-1H-pyrazole and -dimethylamino-4-nitropropiophenone hydrochloride were placed in open Pyrex-glass vessels and irradiated in a domestic microwave oven for 15 s (at 600 W). The reaction mixture was extracted with ethyl acetate and the product was purified by column chromatography on silica gel, using hexane/ethyl acetate (15:1 (v/v) as eluent. Evaporation of the eluate yielded colourless crystals of compound (I) (yield 45%; m.p. 448-450 K) suitable for single-crystal X-ray diffraction, accompanied by a small quantity of the reduced 6-(4-nitrophenyl) derivative, (II). MS (EI 30 eV), m/z (%): 372 (M+, 10), 357, (17), 149 (58), 57 (100).
All H atoms were located in difference maps and then treated as riding atoms, with C-H distances of 0.95 (aromatic) or 0.98 Å (methyl), and with Uiso(H) = 1.2Ueq(C), or 1.5Ueq(C) for the methyl groups.
Data collection: COLLECT (Hooft, 1999); cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: OSCAIL (McArdle, 2003) and SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: OSCAIL and SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 and PRPKAPPA (Ferguson, 1999).
X-ray data were collected at the EPSRC X-ray Crystallographic Service, University of Southampton, England. JC thanks the Consejería de Innovación, Ciencia y Empresa (Junta de Andalucía, Spain) and the Universidad de Jaén for financial support. RA and ER thank COLCIENCIAS and UNIVALLE (Universidad del Valle, Colombia) for financial support.
Ferguson, G. (1999). PRPKAPPA. University of Guelph, Canada.
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Low, J. N., Cobo, J., Nogueras, M., Sánchez, A., Torres, H. & Insuasty, B. (2002). Acta Cryst. C58, o298-o300.
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Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany.
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