Crystal structure of 4-methyl-N-{(E)-methyl[(3aR,8aS)-2-oxo-3,3a,8,8a-tetrahydro-2H-indeno[1,2-d][1,3]oxazol-3-yl]-λ4-sulfanylidene}benzenesulfonamide

The formulation that the title compound, C18H18N2O4S2, adopts is a zwitterionic core with the charge separated to the sulfilimine S and N atoms and is supported by the two different S—N bond distances about the sulfinimine N atom [1.594 (2) and 1.631 (2) Å, respectively] that are typical for such bonds. The notably unusual bond is S—N(oxazolidinone) [1.692 (2) Å] that is longer than a typical S—N bond [1.603 (18) Å, Mogul analysis; Macrae et al. (2008 ▸). J. Appl. Cryst. 41, 466–470]. The bond-angle sum about sulfilimine sulfur (308.35°) reflects the trigonal–pyramidal geometry of this atom. Two of the angles are less than 100°. Despite the pyramidalization of this sulfur, there are no significant intermolecular interactions, beyond usual van der Waals contacts, in the crystal packing.


S1. Commentary
Oxazolidinone sulfilimines are synthesized as precursors of vinyl sulfilimines which are used in the γ-lactamization reaction (Silveira & Marino, 2013) to generate chiral pyrrolidinones with medicinal chemistry interest. This compound represents one of only five other oxazolidinone compounds that incorporate an N-S-N backbone (Barbey et al., 2012;Berredjem et al., 2010;Bonnaud et al., 1987;Dewynter et al., 1997). It is the only reported structure that does not have a sulfonyl bridging the oxazolidinone ring to the second nitrogen atom. Related sulfur-containing oxazolidinones have been reported previously by us (Silveira et al., 2012;2014). We have also reported a related sulfur-containing indole as a precursor of physostigmine alkaloid· .

S2. Synthesis and crystallization
Following literature preparative methods (Celentano et al., 1998;Silveira & Marino, 2013): chloramine-T (951 mg, 4.18 mmol) and hexadecyltributylphosphonium bromide (100 mg, 0.20 mmol) were added to a solution of oxazolidinone sulfide (840 mg, 3.80 mmol) in toluene (25 ml) at 295 K. After overnight stirring, ethyl acetate (25 ml) was added and the mixture washed (2 x 30 ml water; 1 x 30 ml brine), dried over anhydrous sodium sulfate, filtered, and the mixture of solvents rota-evaporated at reduced pressure. To the resulting dry, crude product, silica gel (6 g) and methylene chloride (5 ml) were added and this slurry was rota-evaporated to yield the crude product on silica. This mixture was separated and purified through flash chromatography with elution (70% ethyl acetate / 30% hexanes). After slow evaporation of the ethyl acetate / hexanes elutant, the more polar sulfilimine was obtained as white crystals (688 mg). Two sulfilimine diasterioisomers were obtained in a ratio of 2.5:1 (total of 65% yield).

S3. Refinement details
The structure was modeled routinely with all non-hydrogen atoms included with an anistropic model. Hydrogen atoms were included in calculated positions riding on the atom to which they are bonded (C-H = 0.99 Å for methyl, 0.95 Å for methyne and aromatic. U iso (H) was set = 1.5U eq (C) for methyl and 1.2U eq (C) for all others.
The absolute configuration from synthesis was confirmed by comparison of intensities of Friedel pairs of reflections yielding a Flack x parameter = 0.052 (4) (Parsons et al., 2013) and a Hooft y parameter = 0.050 (6) (Hooft et al., 2008).

Figure 1
Labeling diagram of the title compound. Atomic displacement ellipsoids depicted at the 50% probability level. Hydrogen atoms depicted as spheres of an arbitrary radius.