(2R,3S,4R)-3,4-Isopropylidenedioxy-2-(phenylsulfonylmethyl)pyrrolidin-1-ol

The title compound, C14H19NO5S, was prepared by nucleophilic addition of the lithium derivative of methylphenylsulfone to (3S,4R)-3,4-isopropylidenedioxypyrroline 1-oxide. There are four molecules in the asymmetric unit. The crystal structure determination confirms the configuration of the chiral centres as 2R,3S,4R. In the crystal, pairs of O—H⋯N hydrogen bonds link the molecules into dimers.

The title compound, C 14 H 19 NO 5 S, was prepared by nucleophilic addition of the lithium derivative of methylphenylsulfone to (3S,4R)-3,4-isopropylidenedioxypyrroline 1-oxide. There are four molecules in the asymmetric unit. The crystal structure determination confirms the configuration of the chiral centres as 2R,3S,4R. In the crystal, pairs of O-HÁ Á ÁN hydrogen bonds link the molecules into dimers.
Hydroxylamines are important tools for the synthesis of biologically active compounds (Chevrier et al., 2011;Li et al., 2011).
The title compound, C 14 H 19 NO 5 S, consists of a N-hydroxypyrrolidine ring with a phenylsulfonylmethyl group and an isopropylidenedioxy group as susbtituents. This compound crystallizes in space group P2 1 with four independent molecules (A, B, C and D) in the asymmetric unit which differ slightly in conformation but retain the same (3S,4R) configuration in the acetonide group (Fig. 2). All the bond lengths and angles are within the normal ranges. The C-S-C angles in molecules A, B, C and D are 108.5 (2)°, 104.9 (2)°, 106.4 (2)° and 106.1 (2)°, respectively and the O-S-O angles are 115.6 (3)°, 119.8 (2)°, 116.9 (3)° and 118.3 (2)°, respectively. The large O-S-O angle and this deviation from the optimal 109.5° angle can be explained by the repulsion of the lone pairs of the oxygen placing the oxygen atoms as far away from each other as possible and thus minimizing the C-S-C angle. Torsion-angle differences in molecules A, B, C and D are evident from C6-S1-C7-C8, with values of 78.6 (3)°, 60.6 (3)°, 81.6 (3)° and 60.2 (3)°, respectively. The hydroxyl group at N1 atom is displaced from the planar conformation with the pyrrolidine ring. The O5 -N1-C8-C9 torsion angles are very similar in the four molecules, having values of 165.3 (2)°, 164.6 (2)°, 166.0 (2)° and 163.5 (2)°, respectively.
In the crystal, O-H···N hydrogen bonds between the hydroxyl group and the nitrogen atom of the N-hydroxypyrrolidine link adjacent molecules into dimers (Table 1 and Fig. 3). The dimers form six-membered rings and present an anti-parallel orientation along the [010] direction, as is shown in the crystal packing (Fig. 4).
The stereochemistry of (II) was established studying its NMR spectra and observation of the nOes that this molecule displays. The X-ray analysis corroborated its configuration. Well shaped colourless single crystals were obtained by crystallization from hexane/EtOAc.

Refinement
The hydrogen atoms were positioned geometrically, with C-H distances constrained to 0.93 Å (aromatic), 0.96 Å (methyl), 0.97 Å (methylene) and refined in riding mode with U iso (H) = xUeq(C), where x = 1.5 for methyl H atoms and x = 1.2 for all other H atoms. The hydroxyl hydrogen atoms were positined with an O-H distance of 0.82 Å, starting from the difference Fourier map coordinates and with U iso (H) = 1.5 U eq (O).

Computing details
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 (Sheldrick, 2008).       Crystal packing of C 14 H 19 NO 5 S viewed along a axis, showing intermolecular hydrogen bonding. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.34 e Å −3 Δρ min = −0.38 e Å −3 Absolute structure: Flack (1983), 4863 Friedel pairs Flack parameter: 0.040 (14) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.