6-Bromo-2-(4-nitrophenoxy)-3-(1-phenylethyl)-3,4-dihydro-1,3,2-benzoxazaphosphinine 2-oxide

In the title compound, C21H18BrN2O5P, the six-membered oxazaphosphinine ring is in a twist-boat conformation. One of the phosphoryl O atoms is in an equatorial configuation while the other is axial with respect to the oxazaphosphinine ring. The mean planes of the benzene ring to which the nitro group is attached and the phenyl ring form a dihedral angle of 83.5 (1)°. In the crystal structure, weak intermolecular C—H⋯O hydrogen bonds link the molecules into chains along [100].

In the title compound, C 21 H 18 BrN 2 O 5 P, the six-membered oxazaphosphinine ring is in a twist-boat conformation. One of the phosphoryl O atoms is in an equatorial configuation while the other is axial with respect to the oxazaphosphinine ring. The mean planes of the benzene ring to which the nitro group is attached and the phenyl ring form a dihedral angle of 83.5 (1) . In the crystal structure, weak intermolecular C-HÁ Á ÁO hydrogen bonds link the molecules into chains along [100].

Related literature
For background information on organophosphorus heterocyclic compounds containing O and N in the six membered ring, see: Srinivasulu et al. (2008);Hill (1975); Reddy et al.   Table 1 Hydrogen-bond geometry (Å , ).  (Prasad et al., 2006). Compounds of this class have high anti-tumor activity (Sosnovsky & Paul, 1983), significant bioactivity (Reddy et al., 2004) andmedicinal properties (Hill et al., 1975). In this aspect, the title compound (I) possesses antifungal activity against Aspergillus niger and Alternaria alternata, anti bacterial aganist Gram Positive Bacillus subtilis and Gram negative Escherichia coli and also insecticidal activity against Scirpophaga incertulas (Srinivasulu et al., 2008). These characteristics has motivated us to study the influence of the substituents on the conformation and molecular geometry of the heterocyclic ring in this type of compound.
In the crystal structure (I), the oxazaphosphinine ring adopts a twist boat conformation, with atoms C9/C10/C15/O4 coplanar and the atoms P1 and N2 are displaced in same direction by -0.562 (1) and -0.854 (2)Å respectively. When the substituents at P and N in oxazaphosphinine ring are methoxy phenyl and chloro phenyl, chlorophenoxy and chloro fluorophenyl the conformations are boat and screw boat (Radha Krishna et al., 2007;Krishnaiah et al., 2007). In the present study, the steric and electronic effects of the subsitutents change the conformation of the oxazaphosphinine ring to twist boat and this may be due to nitrophenoxy ring attached to the P atom and phenylethyl substituent at the N atom. The nitrophenoxy and  et al., 1979;Pattabhi et al., 1975). The C-Br bond length [1.895 (2) Å] is in good agreement with the value reported by Radha Krishna et al. (2007). In the crystal structure, molecules are linked by weak intermolecular C-H···O hydrogen bonds (see Table 1

and Fig. 2)
Experimental 4-Nitrophenyl phosphorodichloridate 0.51 g(2.0 mmole)in dry toluene(10 ml) was added dropwise to a stirred solution of 2-[(1-phenylethylamino)methyl] -4-bromophenol 0.61 g (2.0 mmole) and triethylamine 0.40 g (4.0 mmole)in 20 ml of dry toluene at 273K over 20 minutes. After the completion of the addition, the reaction temperature was slowly raised to 328-333K and was maintained at this temperature for 5 h. Progress of the reaction was monitored by TLC using hexane-ethyl acetate (3:1)as mobile phase on silica gel (adsorbent). Upon separation of the triethylamine hydrochloride by filtration and evaporation of the filtrate under reduced pressure, a solid residue was obtained. The residue was washed with water and diffraction quality crystal were grown by slow evaporation of a solution of the title compound in methanol.
supplementary materials sup-2 Refinement H-atoms bound to carbon were positioned geometrically and refined using a riding model with d(C-H) = 0.93 Å, U iso =1.2 eq (C) for aromatic, C-H = 0.980Å U iso =1.2 eq (C) for methine, 0.97 Å, U iso = 1.2 eq (C) for CH 2 group and 0.96 Å, U iso = 1.5 eq (C) for methyl H atoms. Fig. 1. The molecular structure of the title compound. Displacement ellipsoids are drawn at the 40% probability level.