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organic papers
Acta Crystallographica Section E

Structure Reports Online
ISSN 1600-5368

2-(4-Bromophenyl)-5,7-dimethyl[1,3]oxazolo[3,2-a]pyrimidin-4-ium perchlorate

Victor B. Rybakov,* Vadim L. Alifanov and Eugene V. Babaev
Department of Chemistry, Moscow State University, 119992 Moscow, Russian Federation Correspondence e-mail: rybakov20021@yandex.ru

The title compound, C14H12BrN2O+ÑClO4Ð, was synthesized from the parent 2-aminooxazole and acetylacetone and characterized by 1H NMR and single-crystal X-ray diffraction. The bromophenyl fragment and the essentially planar ninemembered bicyclic system form a dihedral angle of 10.50 (11) .

Received 22 September 2006 Accepted 26 September 2006

Comment
Key indicators Single-crystal X-ray study T = 293 K À Mean (C-C) = 0.006 A R factor = 0.045 wR factor = 0.115 Data-to-parameter ratio = 14.7 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e.

In a previous communication (Rybakov et al., 2006b), we reported the crystal structure of 5-(4-bromophenyl)-1,3oxazol-2-amine, (1), prepared by a novel method. Here we report the synthesis and crystal structure of its derivative, 2-(4-bromophenyl)-5,7-dimethyl[1,3]oxazolo[3,2-a]pyrimidin4-ium perchlorate, (2), obtained by condensation of (1) with acetylacetone. Condensation of 2-aminoazoles (azines) with 1,3-dicarbonyl compounds (and their synthetic equivalents) is a well known strategy towards the formation of cationic bicylic systems with a bridgehead N atom. Examples of reactions of this type are known for 2-aminopyridines and 2-amino(benzo)thiazoles (Nesmeyanov & Rybinskaya, 1958; Shulga & Chuiguk, 1971, 1972). There is only one report on the condensation of acetylacetone and 4,5-disubstituted 2aminooxazole derivatives (Chuiguk & Leshenko, 1974). We found that the reaction between acetylacetone and (1) led to the oxazolo[3,2-a]pyrimidinium salt, (2), with good yield. Compound (2) was characterized by 1H NMR.

# 2006 International Union of Crystallography All rights reserved

The bond lengths in the oxazolopyrimidinium ring system of (2) (Fig. 1 and Table 1) confirm its aromatic nature. The dihedral angle between the essentially planar nine-membered bicyclic system and the benzene ring is 10.50 (11) , indicating the presence of conjugation between these aromatic fragments. Similar values for this dihedral angle [3.77 (7) and 5.33 (15) ] were found in previously reported oxazolopyridinium salts (Albov et al., 2004a,b) and in an oxazolopyrimidine salt [1.79 (7) ; Rybakov et al., 2006a]. The positive charge of the cation is concentrated on atom N1, as fairly short intermolecular contacts exist between the cation and the O atoms of the perchlorate anion (having a low-density negative À À charge) [O13ÑÑÑC5 = 2.841 (6) A, O13ÑÑÑN1 = 2.930 (5) A and iii À ; symmetry code: (iii) x, y, z + 1]. O11ÑÑÑC9 = 2.966 (5) A There is a weak C11 H11ÑÑÑO4 intramolecular hydrogen
doi:10.1107/S1600536806039493 Rybakov et al.


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organic papers
Refinement
Refinement on F 2 R[F 2 > 2 (F 2)] = 0.045 wR(F 2) = 0.115 S = 0.96 3090 reflections 210 parameters H-atom parameters constrained w = 1/[ 2(Fo2) + (0.056P)2] where P = (Fo2 + 2Fc2)/3 (Ñ/ )max = 0.001 À Ñmax = 0.35 e A 3 À Ñmin = 0.31 e A 3

Table 1
N1--C5 N1--C9 N1--C2 C2--C3 C3--O4 C3--C10 O4--C5

À Selected geometric parameters (A, ).
1.339 1.376 1.406 1.341 1.390 1.458 1.331 119.9 108.2 131.8 105.6 109.5 132.9 117.6 106.8 122.9 127.3 (5) (4) (4) (5) (5) (5) (4) (3) (3) (3) (3) (3) (4) (3) (3) (3) (4) C5--N6 N6--C7 C7--C8 C7--C71 C8--C9 C9--C91 O4--C5--N1 C5--N6--C7 N6--C7--C8 N6--C7--C71 C8--C7--C71 C9--C8--C7 C8--C9--N1 C8--C9--C91 N1--C9--C91 1.296 1.341 1.403 1.502 1.348 1.478 109.8 114.4 121.8 116.3 121.9 121.6 115.0 127.2 117.8 (5) (5) (6) (6) (6) (6) (3) (4) (4) (4) (4) (4) (4) (4) (4)

Figure 1
The molecular structure of (2), showing the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level with H atoms shown as spheres of arbitrary radius.

bond (Table 2). This same weak interaction is observed in the structures of related oxazolopyridine salts (Albov et al., 2004a,b; Babaev et al., 1997; Babaev, Bush et al., 1999; Babaev, Rybakov et al., 1999) and the oxazolopyrimidine salt (Rybakov et al., 2006a). From a search of the Cambridge Structural Database (Version 5.27; Allen, 2002), we found N HÑÑ ÑN hydrogen bonding for two analogs of the salt (2), viz.6nitro-2-phenylimidazo[1,2-a]pyridine (Aslanov et al., 1983) and 2-phenylimidazo[1,2-a]pyridine (Tafeenko et al., 1996), À with NÑÑÑH distances of 2.53 and 2.50 A, respectively. Weak C HÑÑÑO interactions (Table 2) are observed in the crystal structure of (2).

C5--N1--C9 C5--N1--C2 C9--N1--C2 C3--C2--N1 C2--C3--O4 C2--C3--C10 O4--C3--C10 C5--O4--C3 N6--C5--O4 N6--C5--N1

Table 2

À Hydrogen bond geometry (A, ).
D--HÑÑÑA D--H
i

HÑÑÑA 2. 2. 2. 2. 2. 39 48 52 49 50

DÑÑÑA 3.290 2.812 3.411 3.241 3.402 (6) (5) (6) (6) (6)

D--HÑÑ ÑA 164 101 160 135 156

Experimental
The synthesis of the starting compound, (1), was described by Rybakov et al. (2006a). Concentrated hydrochloric acid (36 ml) and then acetylacetone (22.7 g, 0.228 mol) were added to (1) (18 g, 0.076 mol). The reaction mixture was refluxed for 4 h, keeping the temperature in the range 393 413 K. To the cooled reaction mixture concentrated perchloric acid (20 ml) and diethyl ether (200 ml) were added. The precipitate was filtered off, washed with diethyl ether and ethanol, and recrystallized from acetonitrile (yield 66%, m.p. 588 590 K).

C2--H2ÑÑÑO11 C11--H11ÑÑ ÑO4 C15--H15ÑÑ ÑO11i C91--H91AÑÑ ÑO14 C91--H91CÑÑ ÑO12ii

0.93 0.93 0.93 0.96 0.96
1 2

Symmetry codes: (i) x; y ? 1; z 2

; (ii)

x ? 2; y; z.

Crystal data
C14H12BrN2O+ÑClO4 Mr = 403.62 Monoclinic, P21 =c À a = 15.742 (4) A À b = 13.292 (4) A À c = 7.718 (3) A  = 91.14 (2) À V = 1614.6 (9) A3 Z=4 Dx = 1.660 Mg m 3 Cu K radiation = 5.25 mm 1 T = 293 (2) K Block, colourless 0.15 Ò 0.15 Ò 0.15 mm

À All H atoms were refined using a riding model, with C H 0.93 A À and Uiso(H) 1.2Ueq(C) for aromatic H atoms, and C H 0.96 A and Uiso(H) 1.5Ueq(C) for CH3 H atoms. Data collection: CAD 4 EXPRESS (Enraf Nonius, 1994); cell refinement: CAD 4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP 3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

The authors are indebted to the Russian Foundation for Basic Research for covering the licence fee for use of the Cambridge Structural Database.

Data collection
Enraf Nonius CAD-4 diffractometer ! scans Absorption correction: none 3354 measured reflections 3090 independent reflections 1986 reflections with I > 2 (I) Rint = 0.025 max = 75.0 1 standard reflection frequency: 60 min intensity decay: 7%


References
Albov, D. V., Rybakov, V. B., Babaev, E. V. & Aslanov, L. A. (2004a). Acta Cryst. E60, o1096 o1097. Albov, D. V., Rybakov, V. B., Babaev, E. V. & Aslanov, L. A. (2004b). Acta Cryst. E60, o1301 o1302. Allen, F. H. (2002). Acta Cryst. B58, 380 388. Acta Cryst. (2006). E62, o4809 o4811

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Aslanov, L. A., Tafeenko, V. A., Paseshnichenko, K. A., Bundel, Yu. G., Gromov, S. P. & Gerasimov, B. G. (1983). Zh. Struct. Khim. (Russ.) (J. Struct. Chem.), 24, 115 122. Babaev, E. V., Bozhenko, S. V., Maiboroda, D. A., Rybakov, V. B. & Zhukov, S. G. (1997). Bull. Soc. Chim. Belg. 106, 631 638. Babaev, E. V., Bush, A. A., Orlova, I. A. & Rybakov, V. B. (1999). Tetrahedron Lett. 40, 7553 7556. Babaev, E. V., Rybakov, V. B., Zhukov, S. G. & Orlova, I. A. (1999). Chem. Heterocycl. Compd. 35, 479 485. Chuiguk, V. A. & Leshenko, V. A. (1974). Ukr. Khim. Zh. 40, 633 635; Chem. Abstr. 81, 105438. Enraf Nonius (1994). CAD-4 EXPRESS. Version 5.0. Enraf Nonius, Delft, The Netherlands. Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837 838. Harms, K. & Wocadlo, S. (1995). XCAD4. University of Marburg, Germany. Nesmeyanov, A. N. & Rybinskaya, M. I. (1958). Dokl. Akad. Nauk SSSR, 118, 297 298. (In Russian.) Rybakov, V. B., Alifanov, V. L. & Babaev, E. V. (2006a). Acta Cryst. E62, o4578 o4580. Rybakov, V. B., Alifanov, V. L. & Babaev, E. V. (2006b). Acta Cryst. E62, o4746 o4747 Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of ? Gottingen, Germany. Shulga, S. I. & Chuiguk, V. A. (1971). Ukr. Khim. Zh. 37, 257 260. (In Russian.) Shulga, S. I. & Chuiguk, V. A. (1972). Khim. Geterotsikl. Soedin. 8, 637 640. (In Russian.) Tafeenko, V. A., Paseshnichenko, K. A. & Shenk, H. (1996). Z. Kristallogr. 211, 457 463.

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