Crystal structure of 4-(benzo[d]thiazol-2-yl)-1,2-dimethyl-1H-pyrazol-3(2H)-one

The ring systems of 4-(benzo[d]thiazol-2-yl)-1,2-dimethyl-1H-pyrazol-3(2H)-one are almost coplanar. In the three-dimensional packing, the carbonyl oxygen accepts four weak hydrogen bonds.


Chemical context
Many natural heterocyclic compounds and pharmaceuticals involve benzothiazole moieties and derivatives thereof, which are among the most significant heterocyclic compounds utilized in medicinal chemistry (Bonde et al., 2015).In the search for novel and significant therapeutic drugs, benzothiazoles have a wide range of established pharmacological properties (Wang et al., 2009), and their derivatives include several structural variants (Rana et al., 2008).The application of benzothiazole derivatives in current research and related discoveries is a well-appreciated and quickly growing area of medicinal chemistry (Abdallah et al., 2023).As an example, several drugs based on benzothiazole derivatives have been widely utilized in clinical practice to treat a variety of disorders, with a marked therapeutic efficacy (Huang et al., 2009).
In line with these findings and our prior research (Metwally et al., 2022a,b), the aim of the current investigation was to design and create benzothiazolyl-pyrazole hybrids.The reaction of 2-benzothiazolyl acetohydrazide 1 with N,N-dimethylformamide dimethyl acetal 2 at room temperature led to the synthesis of the unexpected benzothiazole-2-pyrazole derivative 3 in good yield (Fig. 1).The mechanism for the formation of 3 is currently under investigation.In order to establish the structure of the product unambiguously, its crystal structure was determined and is reported here.

Structural commentary
The structure of compound 3 is shown in Fig. 2, with selected molecular dimensions in Table 1.These may be regarded as normal, within the constraints of linked five-membered rings that necessarily lead to narrow angles within the rings and wide exocyclic angles [up to 127.48 (11) � for C10-C8-C2].The molecule is essentially planar (except for the methyl hydrogens); the least-squares plane through all non-H atoms has an r.m.s.d. of only 0.037 A ˚.If the ring systems are regarded separately, the pyrazole and benzothiazole rings have r.m.s.d.values of 0.006 and 0.017 A ˚, respectively, and an interplanar angle of 3.31 (7) � .The coplanarity leads to a short intramolecular contact S1� � �O1 = 2.9797 (10) A ˚.

Supramolecular features
The molecular packing involves five short contacts, four C-H� � �O1 and one C-H� � �S1, that are acceptably linear and may be regarded as 'weak' hydrogen bonds (Table 2).The donor atom H12B is part of a three-centre system with acceptors O1 and S1.The contact H12C� � �O1 is remarkably short at 2.25 A ˚. Additionally, there is a short contact S1� � �N1(x, 3 2 À y, 1 2 + z) = 3.4078 (11) A ˚.A section of the packing is shown in Fig. 3; a ribbon parallel to the b axis and its antiparallel counterpart are shown, which form a double layer parallel to (101).However, the molecules are further linked parallel to the view direction to give a three-dimensional pattern.There are no Cent-Cent contacts shorter than 3.75 A ånd no H� � �Cent contacts shorter than 2.99 A ˚(Cent = ring centroids).

Figure 1
The synthesis of the title compound 3.

Figure 2
The structure of compound 3 in the crystal.Ellipsoids correspond to 50% probability levels.

Figure 3
A section of the three-dimensional packing of compound 3: two antiparallel ribbons viewed perpendicular to (101).Contacts to O1 are shown as thick dashed lines and those to S1 as thin dashed lines.Hydrogen atoms not involved in hydrogen bonding are omitted.The atom labels indicate the asymmetric unit.

Database survey
The search employed the routine ConQuest (Bruno et al., 2002), part of Version 2023.3.0 of the Cambridge Structural Database (Groom et al., 2016).

Synthesis and crystallization
A mixture of 2-benzothiazolyl acetohydrazide 1 (0.01 mol) and N,N-dimethylformamide dimethyl acetal 2 (0.02 mol) was stirred at room temperature for 1 h.The excess acetal was distilled off under reduced pressure; the solid product was washed with a mixture of petroleum ether and diethyl ether (1:1) and then crystallized from ethanol.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3.The methyl groups were included as idealized rigid groups (C-H 0.98 A ˚, H-C-H 109.5 � ) allowed to rotate but not tip (command 'AFIX 137').Other hydrogen atoms were included using a riding model starting from calculated positions (C-H = 0.95 A ˚).The U iso (H) values were fixed at 1.5 � U eq of the parent carbon atoms for the methyl group and 1.2 � U eq for other hydrogens.One reflection clearly in error (F o 2 >> F c 2 ) was omitted from the refinement.

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.

Table 3
Experimental details.