(3S,5R,6S)-Diphenylmethyl 1-oxo-6-bromopenicillanate

In the title compound, C21H20BrNO4S, a key intermediate in the synthesis of the widely used β-lactamase inhibitor tazobactam, the five-membered thiazolidine ring adopts an envelope conformation and the four-membered azetidine ring is in a distorted planar conformation.

In the title compound, C 21 H 20 BrNO 4 S, a key intermediate in the synthesis of the widely used -lactamase inhibitor tazobactam, the five-membered thiazolidine ring adopts an envelope conformation and the four-membered azetidine ring is in a distorted planar conformation. The crystal structure features C-HÁ Á ÁO hydrogen bonds and a weak C-HÁ Á Á interaction.

Structure description
The title compound (Fig. 1) is a key intermediate for the synthesis of tazobactam, a widely used -lactamase inhibitor (Bai et al., 2001). The five-membered thiazolidine ring (N1/C3/C2/S1/C5) adopts an envelope conformation, with an r.m.s deviation of 0.318 Å and a maximum deviation of 0.305 (1) Å for atom S1. The four-membered azetidine ring (N1/C5-C7) is in a distorted planar conformation, with an r.m.s deviation of 0.052 Å . The dihedral angle between the mean planes of these rings is 49.7 (2) . The two phenyl rings of the diphenylmethyl group are inclined at an angle of 79.0 (2) .

Synthesis and crystallization
The title compound, which was a gift sample from Orchid Pharmaceutical Ltd, India, prepared according to the procedure of Xu et al. (2005), was dissolved in acetonitrile. It was heated over a water bath for few minutes and the resultant solution was allowed to cool. After a week, transparent yellow block-shaped crystals separated out. Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the title compound with atom labels and 50% probability displacement ellipsoids.

Figure 2
A partial packing diagram for the title compound. Dashed lines indicate the C-HÁ Á ÁO hydrogen bonds.

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.

data-2
IUCrData (2020). 5, x200143 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.