(Z)-N-[1-(Aziridin-1-yl)-2,2,2-trifluoroethylidene]-4-bromoaniline

The title compound, C10H8BrF3N2, crystallizes with two independent molecules in the asymmetric unit, which can be considered as being related by a pseudo-inversion center, so their conformations are different; the corresponding N=C—N—C torsion angles are 54.6 (5) and −50.5 (5)°. In the crystal, molecules related by translation in [001] interact through short intermolecular Br⋯F contacts [3.276 (2) and 3.284 (2) Å], thus forming two types of crystallographically independent chains.

The title compound, C 10 H 8 BrF 3 N 2 , crystallizes with two independent molecules in the asymmetric unit, which can be considered as being related by a pseudo-inversion center, so their conformations are different; the corresponding N C-N-C torsion angles are 54.6 (5) and À50.5 (5) . In the crystal, molecules related by translation in [001] interact through short intermolecular BrÁ Á ÁF contacts [3.276 (2) and 3.284 (2) Å ], thus forming two types of crystallographically independent chains.

Comment
Aziridines are important heterocyclic compounds present in unusual natural products that display strong biological activity (Tanner, 1994;McCoull & Davis, 2000). For instance, azinomycines A and B isolated from the fermentation broth of Streptomyces griseofuscus and (+)-FR900482 isolated from the culture broth of Streptomyces sandaensis are potent antitumor antibiotics that exhibit exceptional activity against various types of mammalian solid tumors. Mitomycin C is an aziridine-containing antibiotic produced by Streptomyces caespitosus, whose antineoplastic activity is associated with the high reactivity of the strained aziridine ring (Remers & Iyengar, 1995;Armstrong et al., 1996;Katoh et al., 1996). Recently novel types of peptidic cysteine protease inhibitors containing aziridine-2,3-dicarboxylic acid have been designed and synthesized (Schirmeister, 1999a,b).
The title compound I crystallizes in chiral monoclinic space group P2 1 with two crystallographically independent molecules in the unit cell. The two crystallographically independent molecules represent different conformers distinguishing by rotation of the aziridine substituent around the ordinary (CF 3 )C-N bond (the corresponding N1-C1-N2-C3 and N3-C11-N4-C13 totsion angles are 54.6 (5) and -50.5 (5) o , respectively). The bond lengths and angles in I are in a good agreement with those found in the related compounds (Chinnakali et al., 1998;McLaren & Sweeney, 1999;Zhu et al., 2006;Moragas Solà et al., 2010). The molecule of I is the Z-isomer relative to the double C═N bond.
The p-bromo-phenyl substituent is twisted by 38.42 (12) and 39.61 (10)% (for the two crystallographically independent molecules, respectively) relative to the double bond plane. Tha absolute structure of I was objectively determined by the refinement of Flack parameter, which has become equal to 0.025 (11).

Refinement
All hydrogen atoms were placed in the calculated positions with C-H = 0.95 (aryl-H) and 0.99 (methylene-H) Å and refined in the riding model with fixed isotropic displacement parameters: U iso (H) = 1.2U eq (C)]. There are high positive residual densities of 1.44-1.97 eÅ -3 near the Br1 and Br2 centers (0.79-0.90 Å) due to considerable absorption effects which could not be completely corrected.

Figure 1
The synthesis of (Z)-N-[1-(aziridin-1-yl)-2,2,2-trifluoroethylidene]-4-bromoaniline.   Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq