2,3-Dihydropyrrolo[2,1-b]quinazoline-9(1H)-thione

In the crystal, molecules of the title compound, C11H10N2S, are connected by C—H⋯N interactions around threefold axes. Furthermore, they form stacks along the c axis showing π–π interactions between pyrimidine rings [centroid–centroid distance = 3.721 (1) Å]. The central ring is essentially planar with an r.m.s. deviation of 0.007 Å. The five-membered ring adopts an envelope conformation with the flap atom deviating by 0.241 (4) Å from the mean plane (r.m.s. deviation = 0.002 Å) through the other four ring atoms.


Comment
The title compound was synthesized by the reaction of 2,3-dihydro-1H,9H-pyrrolo[2,1-b]quinazolin-9-one with phosphorus pentasulfide ( Figure 1). X-ray single-crystal diffraction study reveals that the title compound crystallizes in the space group R3c with one molecule in the asymmetric unit. The molecule is almost planar (excluding the atom C10) with r.m.s. deviation of 0.014 Å. The central (pyrimidinic) ring is planar with rms deviations of 0.007Å. Conformation of fivemembered (pyrrolic) ring is envelope with deviation of the atom C10 (0.241 (4) Å) from mean plane of other four atoms (rms deviations of 0.002 Å) of the ring. In the structure weak C-H···N interactions (Table 1) are observed. The molecules are stacked along the c axis by π-π stacking interactions between pyrimidine rings [centroid-centroid distances = 3.721 (1) Å].
Experimental 2.5 g (13 mmole) of 2,3-dihydro-1H,9H-pyrrolo[2,1]quinazolin-9-one was dissolved in 15 ml m-xylene and 2.98 g (13 mmole) of phosphorus pentasulfide were added ( Figure 1). Reaction mixture was boiled 2 h and allowed to cool up to room temperature. The precipitate was filtered, flushed with m-xylene (3 ml) and 10% NaOH (50 ml) was added, then the precipittate was filtered and washed with water to get neutral medium and was dried. After recrystallization from hexane 1.96 g (72%) the title compound crystals. Suitable for X-ray diffraction crystals was obtained from hexane with m.p. 138

Refinement
H atoms were positioned geometrically and treated as riding on their C atoms, with C-H distances of 0.93 Å (aromatic)and 0.97 Å (CH 2 ) and were refined with U iso (H)=1.2Ueq(C).

Figure 2
The molecular structure of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.