Crystal structures of (E)-2-amino-4-methylsulfanyl-6-oxo-1-(1-phenylethylideneamino)-1,6-dihydropyrimidine-5-carbonitrile and (E)-2-amino-4-methylsulfanyl-6-oxo-1-[1-(pyridin-2-yl)ethylideneamino]-1,6-dihydropyrimidine-5-carbonitrile

The title compounds differ in the orientations of the phenyl (in 3a) or pyridyl (in 3b) groups. Classical hydrogen bonds involving the amino group lead to one- or two-dimensional packing patterns, respectively.

Pyrimidinones are multipurpose heterocyclic compounds that are common in nucleic acids and find diverse applications in drug planning ; they are important in pharmaceutical chemistry because of their pharmacological potential (Galmarini et al., 2003). Research in the pharmaceutical chemistry of pyrimidone derivatives has become an active field, since several pyrimidinone-based compounds have been extensively used as clinical drugs to treat numerous types of viruses with high therapeutic effectiveness (Simons et al., 2005); their biotic profile and synthetic availability have been attractive in their design and development as possible chemotherapeutics. In particular, pyrimidinone derivatives have recently become significant in the improvement of anti-coronavirus agents (Pruijssers et al., 2019).
In order to access this class of compounds, a variety of new synthetic methods has been developed (Xu et al., 2004). Recently, we have designed the syntheses of several pyrimidinone derivatives starting from activated nitriles (Elgemeie et al., 2015a,b;Abu-Zaied et al., 2020, 2021. As part of this program, the reactions of 2-cyano-N 0 -(1-phenylethylidene)- ISSN 2056-9890 acetohydrazide (1a) or 2-cyano-N 0 -(1-(pyridin-2-yl)ethylidene)acetohydrazide (1b) with 2 in KOH/EtOH were studied. These reactions gave products that were crystallized from DMF and identified by X-ray crystallography as the title compounds (3a,b). 1 H NMR spectra of 3a showed SCH 3 protons at 2.55 ppm and the free NH 2 protons at 8.52 ppm. The formation of 3 from 1 and 2 is assumed to proceed via initial addition of the active methylene group of 1 to the double bond of 2, followed by elimination of CH 3 SH and cyclization via addition of the NH group to the cyano group.

Structural commentary
The structure determinations confirm the expected chemical structures of 3a and 3b; the respective molecules are shown in Figs. 1 and 2. In both compounds, the configuration about the double bond N2 C7 is E and the amino group is planar. The pyrimidine ring dimensions are closely similar; e.g. the shortest bonds are C2-N3, the narrowest angles are at C6 (which bears the oxo substituent) and the widest angles are at C4 (which bears the methylthio group). These and a selection of other dimensions are presented in Tables 1 and 2. The compounds differ chemically only in the phenyl/pyridyl substituents. A least-squares fit of the two molecules shows a moderate difference in the orientation of these groups (Fig. 3, Tables 1 and 2); this may be associated with the role of the pyridyl nitrogen as a hydrogen-bond acceptor in 3b (see below). The structure of compound 3b in the crystal. Ellipsoids correspond to 50% probability levels. Table 1 Selected geometric parameters (Å , ) for 3a.

Figure 3
A least-squares fit of the molecules of 3a (solid bonds) and 3b (dashed bonds; molecule inverted with respect to the deposited coordinates).
Only the fitted atoms are labelled; their r.m.s. deviation is 0.16 Å .

Figure 1
The structure of compound 3a in the crystal. Ellipsoids correspond to 50% probability levels.
Whereas the immediate substituent atoms of the pyrimidine rings lie close to the ring plane for 3a [maximum deviation of 0.103 (2) Å for N6], the substituents O1 and C15 of 3b are more significantly displaced [by 0.203 (2) and 0.179 (3) Å , respectively, to the same side of the ring]. The interplanar angles between the six-membered rings are 56.49 (6) for 3a and 63.12 (3) for 3b.

Supramolecular features
In both structures, the hydrogen atoms of the amino groups act as hydrogen bond donors (Tables 3 and 4). In 3a, neighbouring molecules are connected via the same 2 1 operator, leading to ribbons of molecules parallel to the b axis (Fig. 4). In 3b, one hydrogen bond is formed via a 2 1 and one via an n glide operator, leading to layers parallel to (101) (Fig. 5).

Database survey
A search of the Cambridge Database (ConQuest Version 2.0.5) for 6-oxopyrimidines with the same substitution pattern (N at C2, S at C4, cyano at C5 and N at N1) revealed only our previous structures (Elgemeie et al., 2015a,b;refcodes WUSMAA and WUSMUU); the substituents at N1 were NH-SO 2 -p-C 6 H 4 Br and N CH-2-tht, respectively.

Figure 4
Packing diagram of compound 3a viewed perpendicular to (102) in the region z ' 0.25. Dashed lines indicate classical hydrogen bonds. Hydrogen atoms not involved in such bonds are omitted for clarity.

Figure 5
Packing diagram of compound 3b viewed perpendicular to (101). Dashed lines indicate classical hydrogen bonds. Hydrogen atoms not involved in such bonds are omitted for clarity. was discovered. Despite its less regular reflection shape, the results proved to be slightly better in terms of the wR 2 value, and the results quoted here are for this untwinned crystal.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. The NH hydrogen atoms 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 ). The hydrogens of the aromatic rings were included using a riding model starting from calculated positions (C-H aromatic 0.95 Å ). The U(H) values were fixed at 1.5 (for the methyl H) or 1.2 times the equivalent U iso value of the parent carbon atoms.