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

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.


Experimental
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 electronwithdrawing 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]

Refinement
Hydrogen atoms were included in positions calculated each cycle (C-H = 1.0 Å), and were assigned thermal parameters equal to their bonded atom. The maximum and minimum electron density peaks were located 0.73 and 1.20Å from the Cl2 and Br1 atoms, respectively.
supplementary materials sup-2 Figures   Fig. 1. ORTEPII (Johnson, 1976) plot of (I), with ellipsoids at the 10% probability level. H atoms are drawn as spheres of arbitrary radius.