4,5,8a-Triphenylperhydropyrimido[4,5-d]pyrimidine-2,7-dione monohydrate

The title compound, C24H22N4O2·H2O, was synthesized by the trimethylchlorosilane-catalysed reaction between urea, benzaldehyde and acetophenone. The organic molecule comprises two fused tetrahydropyrimidinone rings with phenyl substituents at the 4- and 5-positions on the tetrahydropyrimidinone rings and a third phenyl substituent at the ring junction 8-position. The 4- and 5-substituted phenyl rings are inclined at a dihedral angle of 22.72 (11)° to one another and make angles of 47.95 (7) and 65.76 (7)° with the third phenyl substituent. In the crystal structure, intermolecular N—H⋯O contacts link pyrimido[4,5-d]pyrimidine molecules into centrosymmetric dimers. Additional N—H⋯O and O—H⋯O hydrogen bonds involving the water molecule generate a three-dimensional network.

The title compound, C 24 H 22 N 4 O 2 ÁH 2 O, was synthesized by the trimethylchlorosilane-catalysed reaction between urea, benzaldehyde and acetophenone. The organic molecule comprises two fused tetrahydropyrimidinone rings with phenyl substituents at the 4-and 5-positions on the tetrahydropyrimidinone rings and a third phenyl substituent at the ring junction 8-position. The 4-and 5-substituted phenyl rings are inclined at a dihedral angle of 22.72 (11) to one another and make angles of 47.95 (7) and 65.76 (7) with the third phenyl substituent. In the crystal structure, intermolecular N-HÁ Á ÁO contacts link pyrimido [4,5-d]pyrimidine molecules into centrosymmetric dimers. Additional N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds involving the water molecule generate a three-dimensional network.   Table 1 Hydrogen-bond geometry (Å , ).  (Agarwal et al., 2005;Gangjee et al., 2005). As a part of our studies on the synthesis of the Biginelli-type compounds (Zhu et al., 2005), the title compound was synthesized by a one-pot three-component reaction between acetophenone, urea and benzaldehyde in presence of trimethylchlorosilane as a catalyst in a yield of 86% ( Fig. 1) (Shi et al., 2007).

Related literature
The bond lengths and angles in the molecule are normal (Allen et al., 1987). The asymmetric unit contains a pyrimidopyrimidine molecule and a solvate water molecule (Fig. 2). The organic molecule comprises two fused tetrahydropyrimidinone rings with phenyl substituents at the 4, and 5 positions on the tetrahydropyrimidinone rings and a third phenyl substituent at the ring junction 8 position. The 4-and 5-substituted phenyl rings are inclined at a dihedral angle of 22.72 (0.11) to one another and make angles of 47.95(0.07) and 65.76(0.07) with the third phenyl substituent.The molecules in the structure are linked via intermolecular N1-H5···O1 and N2-H24···O2 hydrogen bonds. In addition, the molecule is connected to the water molecule by N3-H4···O3, O3-H1···O1 and O3-H2···O2 hydrogen bonds which generate a three dimensional network (Fig. 3).
The product was isolated by filtration through a Büchner funnel and washed first with water, then ethanol. The product was then dried to give a crystalline powder. Colourless, block-shaped single crystals of the title compound were obtained by slow evaporation from ethanol at room temperature.

Refinement
The H atoms bound to C were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.93-0.98 Å and U iso =1.2 or 1.5U eq (parent atom). H atoms bound to the N and water O atoms were found in a difference map and refined freely with isotropic displacement parameters.

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.
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 > 2sigma(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.