Crystal structure of 3-benzyl-2-[(E)-2-(furan-2-yl)ethenyl]-2,3-dihydroquinazolin-4(1H)-one and 3-benzyl-2-[(E)-2-(thiophen-2-yl)ethenyl]-2,3-dihydroquinazolin-4(1H)-one from synchrotron X-ray diffraction

The molecular and crystal structures of two 3-benzyl-2-[(E)-2-(2-aryl)ethenyl]-2,3-dihydroquinazolin-4-ones – products of three-component reactions between benzylamine, isatoic anhydride and furyl- or thienyl-acrolein in the presence of catalytic quantity of p-TsOH – were studied by X-ray diffraction.


Chemical context
The synthesis and chemistry of quinazoline and quinazolinone derivatives have remained at the focus of biochemical research over the past decade owing to their high and diverse physiological activities (for recent reviews, see: Jafari et al., 2016;Wang & Gao, 2013;Selvam & Kumar, 2011). A large part of these studies has been aimed at the development of methods for the synthesis of 2-aryl-substituted quinazolines. However, 2-ethenylquinazolines are much more attractive synthons for subsequent modifications of the heterocyclic skeleton.

Structural commentary
Compounds (I), C 21 H 18 N 2 O 2 , and (II), C 21 H 18 N 2 OS -the products of the three-component reaction between benzylamine, isatoic anhydride and furyl-or thienyl-acrolein are isostructural and crystallize in the orthorhombic space group Pbca (Figs. 2 and 3).
The tetrahydropyrimidine ring in (I) and (II) adopts a sofa conformation, with the C2 carbon atom deviating from the mean plane of the other atoms of the ring by 0.526 (1) and 0.528 (2) Å for (I) and (II), respectively. The nitrogen N1 atom has a trigonal-pyramidal geometry [sum of the bond angles is 347 for both (I) and ( The molecular structure of (I). Displacement ellipsoids are shown at the 50% probability level. H atoms are presented as small spheres of arbitrary radius.

Figure 3
The molecular structure of (II). Displacement ellipsoids are shown at the 50% probability level. H atoms are presented as small spheres of arbitrary radius.
The molecules of (I) and (II) possess an asymmetric center at the C2 carbon atom. The crystals of (I) and (II) are racemates.

Supramolecular features
In the crystals of (I) and (II), molecules form hydrogenbonded helicoidal chains propagating along the [010] direction by strong intermolecular N-HÁ Á ÁO hydrogen bonds (Tables 1  and 2
General procedure. p-TsOH (0.79 g, 4.6 mmol) was added to a mixture of isatoic anhydride (1.5 g, 9.2 mmol), benzylamine (1.2 mL, 11.0 mmol), and furyl-or thienylacrolein (9.2 mmol) in 50 mL EtOH. The reaction mixture was heated under reflux for 4 h. The progress of the reaction was monitored by TLC. When the reaction completed, the mixture was diluted with H 2 O (100 mL) and extracted with EtOAc (3 Â 50 mL). The organic layers were combined, dried (MgSO 4 ), concentrated in vacuo and the residue was purified by column chromatography on SiO 2 (3 Â 20 cm) using hexane and then EtOAc/hexane (1/10!1/5) mixtures as eluent. The resulting product was recrystallized from a mixture of hexane-EtOAc [for (I)] or EtOAc-EtOH [for (II)] to afford the analytically pure samples of the target products.

Figure 4
The crystal structure of (I), demonstrating the hydrogen-bonded helicoidal chains propagating in the [010] direction. Dashed lines indicate the intermolecular N-HÁ Á ÁO hydrogen bonds.

Figure 5
The crystal structure of (II), demonstrating the hydrogen-bonded helicoidal chains propagating in the [010] direction. Dashed lines indicate the intermolecular N-HÁ Á ÁO hydrogen bonds.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. X-ray diffraction studies were carried out on the "Belok" beamline of the National Research Center "Kurchatov Institute" (Moscow, Russian Federation) using a Rayonix SX165 CCD detector. A total of 360 images for each compounds were collected using an oscillation range of 1.0 (' scan mode, two different crystal orientations) and corrected for absorption using the SCALA program (Evans, 2006). The data were indexed, integrated and scaled using the utility iMOSFLM in the CCP4 program (Battye et al., 2011). The hydrogen atoms of the amino groups were localized in difference-Fourier maps and refined isotropically with fixed displacement parameters [U ĩso (H) = 1.2U eq (N)]. The other hydrogen atoms were placed in calculated positions with C-H = 0.95-1.00 Å and refined in the riding model with fixed isotropic displacement parameters [U ĩso (H) = 1.2U eq (C)].
A relatively large number of reflections (a few dozen) were omitted due to the following reasons: (1) In order to achieve better I/ statistics for high-angle reflections we selected a larger exposure time, which resulted in some intensity overloads in the low-angle part of the area. These corrupted intensities were excluded from final steps of the refinement.
(2) In the current setup of the instrument, the low-temperature device eclipses a small region of the detector near its high-angle limit. This resulted in zero intensity of some reflections. (3) In the case of (II), the quality of the single crystal chosen for the diffraction experiment was far from perfect. Some systematic intensity deviations can be due to extinction and defects present in the crystal.  used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2015); software used to prepare material for publication: SHELXTL (Sheldrick, 2015). Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0041 (8) 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.