1-(4-tert-Butylbenzyl)pyrimidine-2,4(1H,3H)-dione

The asymmetric unit of the title compound, C15H18N2O2, contains two independent molecules with essentially identical geometries and conformations. The dihedral angles between the benzene and pyrimidine rings in the two molecules are 89.96 (11) and 73.91 (11)°. The six methyl groups are disordered over two sets of sites, with site occupancies of 0.545 (4):0.455 (4) and 0.542 (7):0.458 (7) in the two molecules. The crystal structure is stabilized by N—H⋯O hydrogen bonds.

anti-AIDS drug (Radatus & Karimian, 1993) and stavudine which is the most widely used anti-HIV drug (Starrett et al., 1992). In order to discover further biologically active pyrimidine compounds, the title compound, (I), was synthesized and its crystal structure determined (Fig. 1).
In the crystal structure of the title molecule, The asymmetric unit contains two independent molecules, with essentially identical geometries and conformations. The dihedral angles between the benzene rings and the pyrimidine rings in the two molecules are 89.96 (0.11) and 73.91 (0.11)°. The six methyl groups are disordered over two positions, with siteoccupancies of 0.545 (4):0.455 (4) and 0.542 (7):0.458 (7) in the two molecules. The crystal structure is stabilized by N -H···O hydrogen bonds. For a crystal structure related to the title compound, see: Li et al. (2005).

Experimental
Uracil (0.56 g, 5 mmol) and anhydrous potassium carbonate (0.84 g, 6 mmol) were mixed in N, N-dimethylformamide (20 ml). A solution of 4-tertbutylbenzyl chloride (0.92 g, 5 mmol) in acetone (10 ml) was then added dropwise, with stirring, at room temperature, and the mixture was stirred for another 10 h and then refluxed for 4 h. The solvent was evaporated in vacuo and the residue was washed with water. The resulting white precipitate was filtered off and purified by column chromatography on silica gel (petroleum ether:ethyl acetate = 2:1). The title compound was recrystallized from ethanol and single crystals of (I) were obtained.

Refinement
All H atoms were placed in calculated positions, with C-H(aromatic) = 0.93 Å and C-H(aliphatic) = 0.96 Å or 0.97 Å, and included in the final cycles of refinement using a riding model, with U iso (H) = 1.2Ueq(C).  The asymmetric unit of the title compound, (I), with displacement ellipsoids drawn at the 30% probability level.  The packing diagram of the title compound. Intermolecular hydrogen bonds are shown as dashed line.

1-(4-tert-Butylbenzyl)pyrimidine-2,4(1H,3H)-dione
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.