Crystal structure of (2R*,3aR*)-2-phenylsulfonyl-2,3,3a,4,5,6-hexahydropyrrolo[1,2-b]isoxazole

A new isoxazolidine has been obtained by 1,3-dipolar cycloaddition of a nitrone and phenyl vinyl sulfone


Chemical context
1,3-Dipolar cycloaddition is one of the most useful reaction in organic synthesis (Pellissier, 2007). Nitrones have been used in the synthesis of many kinds of isoxazolidines (Falkowska et al., 2015) by 1,3-dipolar cycloaddition of nitrones with sulfones (Flores, García, Garrido, Nieto et al., 2012) and have demonstrate a range of biological activities including antibiotic, gene expression regulation and cancer cell cytotoxicity (Karyakarte et al., 2012). Our research group is interested in the synthesis of isoxazolidines such as the title compound, for application in organic synthesis (Flores et al., 2011a,b;Flores et al., 2013).

Structural commentary
The molecular structure of the title compound, which consists of an anisoxazol derivative with a phenyl sulfone group as substituent, is shown in Fig. 1. Both the fused five-membered rings assume a twist conformation, as indicated by puckering parameters Q = 0.338 (3) Å , ' = À73.5 (7) for the pyrrole ring and Q = 0.209 (2) Å , ' = À97.5 (6) for the isoxazole ring. The dihedral angle between the mean planes of the five-membered rings is 64.91 (10) . All the bond lengths are within normal ranges. The C-S-C and O-S-O angles are 104.34 (9) and 118.54 (11) , respectively. The large O-S-O angle, and its deviation from the ideal 109.5 angle, can be explained by the repulsion of the lone pairs of the oxygen atoms as far away from each other as possible minimizing the C-S-C angle. The C5-C6-S1-C7 torsion angle is 171.26 (15) .

Supramolecular features
In the extended structure of the title compound, intermolecular C-HÁ Á ÁO hydrogen bonds involving the O1 isoxazole and the O3 phenyl sulfone O atoms as donors (Table 1) lead to molecular chains running parallel to the b axis (Fig. 2).

Figure 2
Crystal packing of the title compound viewed along the [100] direction, showing intermolecular hydrogen bonding (dashed lines).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The hydrogen atoms were positioned geometrically, with C-H distances constrained to 0.93 Å (aromatic CH), 0.97 Å (methylene CH 2 ), 0.98 (methyne CH) and refined using a riding mode with U iso (H) = 1.2U eq (C). Data collection: APEX2 (Bruker 2006); cell refinement: SAINT (Bruker 2006); data reduction: SAINT (Bruker 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXTL/PC (Sheldrick, 2008). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.23 e Å −3 Δρ min = −0.25 e Å −3 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.