An Optimized Synthesis, Molecular Structure and Characterization of Benzylic Derivatives of 1,2,4-Triazin-3,5(2H,4H)-dione.

4-Benzyl-1,2,4-triazin-3,5(2H,4H)-dione (3-benzyl-6-azauracil, 2), and 2,4-dibenzyl-1,2,4-triazin-3,5(2H,4H)-dione (1,3-dibenzyl-6-azauracil, 3) were synthesized by the reaction of 1,2,4-triazin-3,5(2H,4H)-dione (6-azauracil, 1) with benzyl bromide and potassium carbonate in dry acetone via the 18-crown-6-ether catalysis. In these reaction methods, we developed more convenient and efficient methodologies to afford compounds 2 and 3 in good yields. These compounds were characterized by H-1- and C-13-NMR, MS spectrum, IR spectroscopy and elemental analysis. The structure of 2 was verified by 2D-NMR measurements, including gHSQC and gHMBC measurements. A single-crystal X-ray diffraction experiment indicated that compound 3, with the molecular formula C17H15N3O2, crystallized from a CH3OH/CH2Cl2 diffusion solvent system in a monoclinic space group P2(1)/c with a = 13.7844(13), b = 8.5691(8), c = 13.0527(12) angstrom, beta = 105.961(2)degrees, V = 1482.3(2) angstrom(3), Z = 4, resulting in a density D-calc of 1.314 g/cm(3). The crystal structure of compound 3 is tightly stabilized by contact with five other molecules from the six short contacts formed by intermolecular C-O center dot center dot center dot H-Car, C-H center dot center dot center dot Car, and weakly pi center dot center dot center dot pi stacking interactions. The dihedral angle 31.90 degrees is formed by the mean planes of the benzene rings of the N-2 and N-4 benzyl groups.