2,8-Dibromo-4,10-dichloro-6H,12H-5,11-methano­dibenzo[b,f][1,5]diazo­cine

Kai-Xian Zhu; Donald C Craig; Andrew C Try

doi:10.1107/S1600536808026226

. 2008 Aug 20;64(Pt 9):o1797. doi: 10.1107/S1600536808026226

2,8-Dibromo-4,10-dichloro-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine

Kai-Xian Zhu ^a, Donald C Craig ^b, Andrew C Try ^a,^*

PMCID: PMC2960512 PMID: 21201776

Abstract

The title compound, C₁₅H₁₀Br₂Cl₂N₂, a 2,8-dibromo-4,10-dichloro Tröger’s base analogue derived from 4-bromo-2-chloroaniline, has a dihedral angle of 110.9 (10)° between the two aryl rings, the largest yet measured for a simple dibenzo analogue.

Related literature

For related literature on the synthesis and crystal structures of dihalogenated Tröger’s base analogues, see: Jensen & Wärnmark (2001 ▶); Faroughi et al. (2006a ▶, 2007a ▶,b ▶). For Tröger’s base analogues substituted with multiple electron-withdrawing groups, see: Faroughi et al. (2006b ▶); Bhuiyan et al. (2006 ▶, 2007 ▶); Vande Velde et al. (2008 ▶). For reactions of halogenated Tröger’s base analogues, see: Jensen et al. (2002 ▶); Hof et al. (2005 ▶). For literature on racemization of Tröger’s base analogues and the effect of substituents ortho to the diazocine N atoms, see: Lenev et al. (2006 ▶).

Experimental

Crystal data

C₁₅H₁₀Br₂Cl₂N₂
M _r = 449.0
Orthorhombic,
a = 7.910 (2) Å
b = 12.601 (3) Å
c = 15.230 (4) Å
V = 1518.0 (7) Å³
Z = 4
Mo Kα radiation
μ = 5.64 mm⁻¹
T = 294 K
0.30 × 0.12 × 0.07 mm

Data collection

Enraf–Nonius CAD-4 diffractometer
Absorption correction: analytical (de Meulenaer & Tompa, 1965 ▶) T _min = 0.52, T _max = 0.69
1394 measured reflections
1394 independent reflections
1028 reflections with I > 2σ(I)
1 standard reflection frequency: 30 min intensity decay: none

Refinement

R[F ² > 2σ(F ²)] = 0.056
wR(F ²) = 0.061
S = 1.61
1394 reflections
189 parameters
H-atom parameters constrained
Δρ_max = 0.98 e Å⁻³
Δρ_min = −1.02 e Å⁻³
Absolute structure: Flack (1983 ▶)
Flack parameter: 0.09 (2)

Data collection: CAD-4 (Schagen et al., 1989 ▶); cell refinement: CAD-4; data reduction: local program; program(s) used to solve structure: SIR92 (Altomare et al., 1994 ▶); program(s) used to refine structure: RAELS (Rae, 1996 ▶); molecular graphics: ORTEPII (Johnson, 1976 ▶); software used to prepare material for publication: local programs.

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808026226/tk2290sup1.cif

e-64-o1797-sup1.cif^{(19.8KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808026226/tk2290Isup2.hkl

e-64-o1797-Isup2.hkl^{(51.8KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

The authors thank Macquarie University for the award of a Macquarie University Research Development Grant to ACT.

supplementary crystallographic information

Comment

Tröger's base analogues bearing electron-withdrawing groups were long thought to be difficult, if not impossible, to prepare. However, the synthesis of dihalogenated (Jensen & Wärnmark, 2001), octafluoro (Vande Velde et al., 2008) and tetranitro (Bhuiyan et al., 2007) Tröger's base analogues highlight the possiblities that now exist in terms of incorporating electron-withdrawing groups on the starting anilines. The synthetic utility of halogen-substituted Tröger's base analogue has been demonstrated with their conversion to alkyne- (Jensen & Wärnmark, 2001; Jensen et al., 2002) and functionalized phenyl- (Hof et al., 2005) substituted analogues, among others. It is noteworthy that crystal structures of several other 2,4,8,10-tetrasubstituted Tröger's base analogues exhibit large dihedral angles that are close to that in (I). Tröger's base analogues are known to undergo racemization in acidic solution, however the presence of a substituent at the ortho-position, relative to the bridge nitrogen atoms, has been shown to increase the racemization barrier (Lenev et al., 2006).

The molecular structure of (I) is shown in Fig. 1 and it was prepared as outlined in Fig. 2.

Experimental

4-Bromo-2-chloroaniline (1 g, 4.84 mmol) and paraformaldehyde (232 mg, 7.74 mmol) were added to an ice-cold solution of trifluoroacetic acid (10 ml). The reaction mixture was then stirred in dark at room temperature for 7 days under an atmosphere of argon. The ice-cold reaction mixture was basified by the dropwise addition of a mixture of ammonia (28%, 20 ml) and water (40 ml), followed by the additon of a saturated sodium hydrogen carbonate solution (20 ml). The resultant mixture was then extracted with dichloromethane (3 x 20 ml) and the combined organic layers were washed with brine (40 ml), dried over anhydrous sodium sulfate, filtered and evaporated to dryness. The crude product was chromatographed (silica gel, dichloromethane:hexane 8:2) to afford 2,8-dibromo-4,10-dichloro-6H,12H-5,11-methanodibenzo [b,f][1,5]diazocine (I) (613 mg, 56%) as a white solid and as a racemic mixture: m.p. 471–472 K; ¹H NMR (400 MHz, CDCl₃) δ 4.21–4.33 (4H, m), 4.55 (2H, d, J 17.3 Hz), 7.04 (2H, d, J 2.1 Hz), 7.41 (2H, d, J 2.1 Hz); ¹³C NMR (100 MHz, CDCl₃) δ 54.37, 67.32, 117.15, 128.49, 130.17, 131.02, 131.71, 142.33. Analysis found: C 40.46; H 2.22; N 6.46; C₁₅H₁₀Br₂Cl₂N₂ requires C 40.13; H 2.25; N 6.24. Single crystals were obtained from slow evaporation from dichloromethane solution of (I).