2-Propyl 3,3-dibromo-2-hydroxypyrrolidine-1-carboxylate

The title compound, C8H13Br2NO3, crystallizes as a non-merohedral twin with twin law −0.6 0 0.4/0 − 1 0 /1.6 0 0.6, and the structure has a refined twin domain ratio of 0.546 (5). The structure shows a compact conformation, with the ester unit roughly coplanar with a mean plane fitted through the non-H atoms of the pyrrolidine ring [dihedral angle = 8.23 (9)°]. In the crystal, inversion dimers linked by pairs of O—H⋯O hydrogen bonds generate an R 2 2(12) motif.

The title compound, C 8 H 13 Br 2 NO 3 , crystallizes as a nonmerohedral twin with twin law À0.6 0 0.4/0 À 1 0 /1.6 0 0.6, and the structure has a refined twin domain ratio of 0.546 (5). The structure shows a compact conformation, with the ester unit roughly coplanar with a mean plane fitted through the non-H atoms of the pyrrolidine ring [dihedral angle = 8.23 (9) ]. In the crystal, inversion dimers linked by pairs of O-HÁ Á ÁO hydrogen bonds generate an R 2 2 (12) motif.

Comment
We are working to develop new synthetic methodology by application of hypervalent iodine reagents (oxidation state III) in conjunction with bromotrimethylsilane (TMSBr). Specifically, iodosobenzene (Magnus et al., 1994) or iodobenzenediacetate in the presence of TMSBr promotes controlled formation of an oxidized product in one pot, derived from cyclic amides.
The transformation represents an α, β, β oxidative process, and the yield of the product, (I), was optimized by varying reaction parameters (Salamant & Hulme, 2006). The structure of this molecule generated from one simple microwave-assisted protocol was confirmed by X-ray crystallography.
The molecular structure of (I) is shown in Fig. 1. Molecular dimensions are unexceptional and the compound has a compact conformation; as evidenced by the torsion angle C2-N-C5-O2 = 0.1 (2)° the ester moiety is essentially coplanar with the pyrrolidine ring. Furthermore the angle between a least-squares plane fitted through all non-hydrogen atoms of the pyrrolidine ring (r.m.s. deviation = 0.1666 Å) and the ester moiety (r.m.s. deviation = 0.0226 Å) is 8.23 (9)°. The pyrrolidine ring adopts an envelope conformation with a Cremer-Pople puckering parameter Q of 0.4053 (15) Å (Cremer & Pople, 1975). The compound forms a hydrogen-bonded dimer by means of an R 2 2 (12) motif ( Fig. 2; Bernstein et al., 1995) although there is no further hydrogen bonding in the crystal structure.

Refinement
The crystal used was a two-component non-merohedral twin. The two components of the diffraction pattern were easily separated using CELL_NOW (Sheldrick, 2004) Fig. 1. The molecular structure of (I) with anisotropic displacement ellipsoids at the 50% probability level. Fig. 2. An a-axis packing plot of (I). Blue dotted lines indicate hydrogen bonds; red dotted lines indicate hydrogen bond continuation. 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.

2-
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 Rfactors(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