2,3-Trimethylene-7,8-dihydropyrrolo[1,2-a]thieno[2,3-d]pyrimidin-4(6H)-one

The title molecule, C12H12N2OS, is planar, with an r.m.s. deviation of 0.04 Å. In the crystal, the N atom adjacent to the carbonyl group is sp 2-hybridized. The crystal structure is stabilized by π–π stacking interactions observed between thiophene and pyrimidinone rings of c-glide-related molecules [centroid–centroid distance = 3.9554 (13) Å] and by C—H⋯π interactions, forming an infinite chain along the c-axis direction.

The title molecule, C 12 H 12 N 2 OS, is planar, with an r.m.s. deviation of 0.04 Å . In the crystal, the N atom adjacent to the carbonyl group is sp 2 -hybridized. The crystal structure is stabilized bystacking interactions observed between thiophene and pyrimidinone rings of c-glide-related molecules [centroid-centroid distance = 3.9554 (13) Å ] and by C-HÁ Á Á interactions, forming an infinite chain along the c-axis direction.
Interaction of ethyl 2-amino-4,5-trimethylene-thiophene-3-carboxylate with γ-butyrolactam in presence of phosphorus oxycloride leads to the formation of a new potentially active tetracyclic thieno[2,3-d] pyrimidin-4-one. Synthesis of the title compound was carried out at 368-371 K with reagents in the ratio ester:lactam:POCl 3 of 1:1.5:3.6. The structure of the synthesized compound has been investigated by XRD analysis.
The molecular structure of the title compound is shown in Fig. 2. As shown in the picture, the molecule of the title compound is planar with r.m.s. deviation of 0.04 Å (non-hydrogen atoms). The sum of bond angles of atom N5 (close to 360°) and bond lengths indicate sp 2 hybridization of the nitrogen atom. This indicates that the lone electron pair of N5 atom participates in a conjugation with π-electrons of carbonyl group (C4═O1).

Experimental
The title compound was synthesized on the basis of a well-known method (Elmuradov, et al., 2011) (Fig. 2). Light yellow crystals suitable for X-ray analysis (in the form of prisms with size 0.20x0.17x0.15 mm) were obtained from DMSO solvent at room temperature, m.p. 475-476 K.

Refinement
The hydrogen atoms were placed geometrically (with C-H distances of 0.97 Å for CH 2 ) and included in the refinement in a riding motion approximation with U iso =1.2U eq (C).

Figure 2
Reaction scheme for the formation of the title compound. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.