Crystal structure of ethyl 2-(3-amino-5-oxo-2-tosyl-2,5-dihydro-1H-pyrazol-1-yl)acetate

The N-substituents lie on opposite sides of the pyrazole ring. Intermolecular hydrogen bonds from the amino group to an S=O group and to the oxo substituent lead to a layer structure.

In the title compound, C 14 H 17 N 3 O 5 S, the five-membered ring is essentially planar. The substituents at the nitrogen atoms subtend a C-N-N-S torsion angle of À95.52 (6) . The amino group forms an intramolecular hydrogen bond to a sulfonyl oxygen atom; two intermolecular hydrogen bonds from the amino group, to the other S O group and to the oxo substituent, form a layer structure parallel to the ab plane. The structure determination confirms that the title compound is N-rather than O-alkylated.

Chemical context
Recently we have been attempting to develop synthetic strategies for heterocyclic ring systems containing N-sulfonylamino-and N-sulfonyl moieties. The products may be biologically active, displaying for instance anti-viral activity (Azzam et al., 2017(Azzam et al., , 2020Zhu et al., 2013;Elgemeie et al., 2017Elgemeie et al., , 2019. Also, some of our reported N-arylsulfonylpyrazole derivatives (Elgemeie et al., 1998(Elgemeie et al., , 2013Elgemeie & Hanfy, 1999) proved to be inhibitors of the NS2B-NS3 virus and the enzyme cathepsin B16 (Myers et al., 2007;Sidique et al., 2009). In a continuation of our research investigating new approaches to other new derivatives of N-sulfonylpyrazoles, seeking various scaffolds for use as encouraging chemotherapeutics (Zhang et al., 2020;Elgemeie & Jones, 2002), we have now synthesized the N1-substituted derivative of N-sulfonylpyrazole 1 (the structure of which we have reported; Elgemeie et al., 2013).
The reaction of 1 with ethyl bromoacetate 2 in dry N,Ndimethylformamide containing anhydrous potassium carbonate at room temperature afforded a product for which two possible isomeric structures, the N-alkylated or O-alkylated Nsulfonylpyrazoles 3 or 4, were feasible. The 1 H NMR spectrum of the product showed four singlet signals at = 2.41, 4.31, 4.40 and 7.15 ppm assigned to CH 3 , pyrazole-CH, CH 2 and NH 2 protons, along with triplet and quartet signals at = 1.17 and 4.09 ppm, assigned to ethyl groups. The spectroscopic data cannot differentiate between structures 3 and 4. We therefore determined the X-ray structure of this product, which proved to be the N-alkylated-N-sulfonylpyrazole 4.

Structural commentary
The molecule of compound 4 is shown in Fig. 1. Molecular dimensions, a selection of which are presented in Table 1, may be considered normal (e.g. the N1-N2 bond length corresponds to a single bond and these atoms display a pyramidal geometry). The substituents S1 and C6 of the five-membered ring, which is effectively planar (r.m.s. deviation 0.026 Å ) lie significantly outside the ring plane [by 1.2344 (8) and 0.8468 (19) Å , respectively] in opposite directions; the corresponding torsion angle C6-N1-N2-S1 is À95.52 (6) . The side chain at N1 exhibits an extended conformation. An intramolecular hydrogen bond is formed from the amino group to the sulfonyl oxygen atom O4 ( Table 2). The ring planes subtend an interplanar angle of 57.01 (3) .

Database survey
A database search (CSD Version 5.41) for the same ring system as in 4, and bearing the same substituents at C5 (oxo) and C3 (amino), gave eight hits involving uncharged species. However, none of these was substituted at both ring nitrogen

Figure 2
Packing diagram of compound 4 viewed perpendicular to the ab plane in the region z ' 0.25. Dashed lines indicate hydrogen bonds. Hydrogen atoms not involved in hydrogen bonding are omitted for clarity.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The hydrogen atoms of the NH 2 group were refined freely. The methyl groups were refined as idealized rigid groups allowed to rotate but not tip (AFIX 137; C-H = 0.98 Å , H-C-H = 109.5 ). Other hydrogens were included using a riding model starting from calculated positions (C-H aromatic = 0.95, C-H methylene = 0.99 Å ). The U iso (H) values were fixed at 1.5 (for the methyl H) or 1.2 times the equivalent U eq value of the parent carbon atoms.  (Siemens, 1994); software used to prepare material for publication: SHELXL2018/3 (Sheldrick, 2015b).