Title compounds are obtained by reaction of guanidine derivatives with alkyl and aryl aldehydes.

A practical synthesis of 3,4-dihydro pyrimido[1,2-a][1,3,5]triazin-6-ones, experimental and theoretical assessment of their tautomeric preferences and biological activity results are presented.

AbstractNovel thermal rearrangements are presented.

A novel thermal rearrangement, involving pyrimidine ring opening and subsequent ring closure leading to recyclization of the system, was identified in the reaction of (6-oxo-1,6-dihydropyrimidin-2-yl)guanidines 3 (where NR(1)R(2) = NH(2), NH alkyl, NH aralkyl, NHCH(2)Ph(R)) with triethyl orthoacetate, affording 4-substituted-2-methyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-ones 6 and their ring opened products. However, no such rearrangement was observed with (6-oxo-1,6-dihydropyrimidin-2-yl)guanidines 3 bearing a tertiary amino or anilino substituent (i.e. where NR(1)R(2) = N(CH(3))(2), indoline, morpholino, NHAr). As expected, 2-substituted-4-methyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-ones 4 were obtained as the final products. Experimental structural determination and theoretical studies were carried out to get an understanding of the observed thermal rearrangement. In addition, an attempt to obtain similar pyrimido[1,2-a][1,3,5]triazin-6-ones using N,N-dimethylacetamide dimethyl acetal (DMA-DMA) as one carbon inserting synthon had furnished triazine ring annulated product 14 bearing N,N-dimethyl enamino substituent at position 4 as a result of further reaction with a second molecule of DMA-DMA.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

In the title compound, C8H9N5O, the mean planes through the pyrimidine and triazine rings form a dihedral angle of 2.83 (16)degrees. The amino group adopts a trigonal-planar configuration and forms an intramolecular resonance-assisted N-H...O=C hydrogen bond with the carbonyl group. In the crystal, molecules are linked via intermolecular N-H...N hydrogen bonds into chains of C (2) 2(6)[R (2) 2(6)] motif. The molecules form two types of sheet parallel to (201) and ( (1) over bar 01), respectively.

In the title compound, C8H9N5O, the mean planes through the pyrimidine and triazine rings form a dihedral angle of 2.83 (16)°. The amino group adopts a trigonal-planar configuration and forms an intramolecular resonance-assisted N—H...O=C hydrogen bond with the carbonyl group. In the crystal, molecules are linked via intermolecular N—H...N hydrogen bonds into chains of C22(6)[R22(6)] motif. The molecules form two types of sheet parallel to (201) and (overline{2}01), respectively.

From the reaction of biguanide with ethyl benzoylacetate, N-(6-oxo-4-phenyl-1,6-dihydropyrimidin-2-yl)guanidine (1) and 6-benzoylmethyl-1,3,5-triazin-2,4-diamine (2) were isolated. The structural evaluation of 2 was performed theoretically (DFT calculations) and experimentally (NMR spectroscopy and X-ray crystallography). The effects of solvents and temperature on keto-enol-enaminone tautomeric equilibrium were explored.

The title compound, C(13)H(9)BrF(3)N(5)O, crystallizes with two independent mol-ecules in the asymmetric unit. The pyrimidine rings of the mol-ecules are planar [maximum deviations 0.053 (3) and 0.012 (3) Å], while the triazine rings adopt flattened half-boat conformations with the p-bromo-phenyl rings in the flagpole positions. The crystal packing is stabilized by a three-dimensional network of inter-molecular N-H⋯N, N-H⋯O and N-H⋯F hydrogen bonds.

The title compound, C13H9BrF3N5O, crystallizes with two independent molecules in the asymmetric unit. The pyrimidine rings of the molecules are planar [maximum deviations 0.053 (3) and 0.012 (3) Å], while the triazine rings adopt flattened half-boat conformations with the p-bromophenyl rings in the flagpole positions. The crystal packing is stabilized by a three-dimensional network of intermolecular N—H...N, N—H...O and N—H...F hydrogen bonds.

The cyclocondensation reaction of N-(4-methyl-6-oxo-1,6-dihydropyrimidin-2-yl)guanidine with benzaldehyde was found to result in the formation of 2-amino-4-phenyl-4,6-dihydro-1(3)(9)H-pyrimido[1,2-a][1,3,5]triazin-6-one. The reaction proceeded chemo- and regioselectively affording the 1,3,5-triazine ring closure at nitrogen atom adjacent to carbonyl group. The structure of 2-amino-4-phenyl-4,6-dihydro-1(3)(9)H-pyrimido[1,2-a][1,3,5]triazin-6-one was supported by 1H,13C NMR and 2D NOESY spectral data. From the experimental data, 3H- tautomeric form seemed to be predominant in DMSO-d6 solution. The relative energies of the tautomers were estimated using calculations at different levels of theory (HF/6-311G**, B3LYP/6-311++G** and MP2/6-311++G**). Both the experimental and theoretical results excluded 6-hydroxy tautomer from the equilibrium. 2-Amino-4-phenyl-4,6-dihydro-1H-pyrimido[1,2-a][1,3,5]triazin-6-one was calculated to be the energetically preferred tautomeric form in gas phase.