Crystal structure of 2-(benzo[d]thiazol-2-yl)-3,3-bis(ethylsulfanyl)acrylonitrile

The double-bond system of the acrylonitrile moiety is significantly non-planar and displays one very wide angle C—C(CN)=C.

In the title compound, C 14 H 14 N 2 S 3 , the double-bond system of the acrylonitrile moiety is significantly non-planar, with absolute cis torsion angles of 13.9 (2) and 15.1 (2) . The ring system and the double bond system subtend an interplanar angle of 11.16 (4) . The wide angle C-C(CN) C of 129.40 (12) may be associated with a balance between planarity and avoidance of a very short SÁ Á ÁS contact.

Chemical context
Research into medicinal chemistry based on benzothiazoles has become a fast developing and progressively more active topic. The high degree of structural diversity has proved to be important in the search for new effective treatments (Ammazzalorso et al., 2020;Elgemeie, 1989). A large number of therapeutic agents based on benzothiazole systems have been synthesized and evaluated in terms of their pharmacological properties (Gill et al., 2015;. Much information about benzothiazoles has been reported in the scientific literature, describing their anti-inflammatory, antimicrobial, neuroprotective, anticonvulsant and antiproliferative effects (Seenaiah et al., 2014). The molecular mechanisms responsible for this variety of pharmacological activity have not been completely established, and various biological pathways have been indicated as possible targets of this class of molecules (Keri et al., 2015). We are engaged in developing synthetic strategies for benzothaizole systems that show important biological activity as novel antimicrobial and antiviral agents (Azzam et al. 2017a(Azzam et al. ,b, 2020a(Azzam et al. ,b,c, 2021Elgemeie et al., 2000a,b;. As an extension of this research Elgemeie & Elghandour, 1990), we report here a novel benzothiazole cyanoketene dithioacetal (2). Compound 2 was synthesized by the reaction of 2-cyanomethylbenzothiazole 1 with carbon disulfide in the presence of sodium ethoxide, followed by alkylation with ethyl iodide. The structure of 2 was originally based on its elemental analysis and spectroscopic data (see Experimental). In order to establish the structure of the compound unambiguously, the crystal structure was determined.

Structural commentary
The molecule of 2 is shown in Fig. 1. The heterocyclic system is coplanar to within an r.m.s. deviation of only 0.007 Å , and its dimensions are as expected (a selection of molecular dimensions are presented in Table 1). There is appreciable twisting of ca 14 about the double bond C8 C9 (see torsion angles in Table 1), so that the 'plane' of the atoms C2, C8, C9, C10, S2 and S3 displays an r.m.s. deviation of 0.14 Å ; the two planes subtend an interplanar angle of 11.16 (4) . The angle C2-C8 C9 (formally sp 2 ) is strikingly wide, at 129.40 (12) ; for comparison, the corresponding angles in the five structures mentioned below (with refcodes) range from 122-126 . One might speculate that this large angle and the deviation from planarity about the double bond represent aspects of a compromise between (i) achieving coplanarity of the heterocycle with the double-bond system and (ii) avoiding too short an SÁ Á ÁS contact. The intramolecular SÁ Á ÁS distances are S1Á Á ÁS3 = 3.1155 (5) and S2Á Á ÁS3 = 3.0496 (5) Å . The ethyl groups project to opposite sides of the molecule.

Supramolecular features
The molecular packing is fairly featureless; a general view is given in Fig. 2 and some borderline possible 'weak' hydrogen bonds are listed in Table 2. The main feature is the loose association of pairs of molecules across inversion centres, whereby the heterocyclic systems face each other; however, there is a considerable offset. The centroids of the fivemembered rings lie 3.72 Å apart, and the shortest contact is C7AÁ Á ÁC7A 0 (operator 1 À x, 1 À y, 1 À z) 3.741 (2) Å . The sulfur atom S1 lies 3.61 Å from the centroid of the sixmembered ring in the facing molecule; such potential SÁ Á Á interactions have been discussed by e.g. Ringer et al. (2007) and Silva et al. (2018).
(0.04 mol) was added gradually and then the solution was warmed for 20 min. Ethyl iodide (0.08 mol) was then added, and the reaction mixture was stirred overnight at room temperature. The solution was poured onto ice-water and the solid product thus formed was filtered off. The product was purified by dissolving it in hot petroleum ether, filtering, and allowing the solution to cool.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The methyl groups were refined as idealized rigid groups allowed to rotate but not tip, with C-H = 0.98 Å and H-C-H = 109.5 . Other hydrogen atoms were included using a riding model starting from calculated positions (C-H aromatic = 0.95, C-H methylene = 0.99 Å ). The U(H) values were fixed at 1.5 or 1.2 times the equivalent U iso value of the parent carbon atoms for methyl and non-methyl hydrogen atoms, respectively.  (Sheldrick, 2015) and XP (Siemens, 1994).

Figure 2
Crystal packing of 2 viewed parallel to the a axis (hydrogen atoms omitted for clarity). The loose association of the heterocyclic systems across inversion centres can be recognized in the central horizontal rows of rings.  (Agilent, 2014); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015); molecular graphics: XP (Siemens, 1994); software used to prepare material for publication: SHELXL2018/3 (Sheldrick, 2015).

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.