Condensation of s-substituted 6-amino-2-thiouracils with benzaldehydes

In the present study 5,5'-(phenylmethylene) bis (2-organylsulfanyl-6-aminopyrimidin-4(3 H )-ones) were obtained by the interaction of 2-allylsulfanyl-, 2-methallylsulfanyl- and 2-propargylsulfanyl-6-aminopyrimidin-4(3 H )-ones with benzaldehyde with ratio of 2:1 in concentrated acetic acid at room temperature. At the same conditions 5,5'-((4-(dimethylamino)phenyl)methylene) bis (2-organylsulfanyl-6-aminopyrimidin-4(3 H )-ones) and 5,5'-((3,4-dimethoxyphenyl)methylene) bis (2-benzylsulfanyl-6-aminopyrimidin-4(3 H )-one) were prepared by the reaction of 2-allylsulfanyl-, 2-benzylsulfanyl-, 2-propargylsulfanyl-6-aminopyrimidin-4(3 H )-ones with 4,4-dimethylaminobenzaldehyde and 2-benzylsulfanyl-6-aminopyrimidin-4(3 H )-one with 3,4-dimethoxybenzaldehyde, respectively. The initial 2-organylsulfanyl-6-aminopyrimidin-4(3 H )-ones were prepared by the known method of 6-amino-2-thiouracil alkylation by organylhalides (allyl bromide, methallyl chloride, propargyl bromide, benzyl chloride) in aqueous ethanol at room temperature in the presence of alkali. The structures of dipyrimidines were confirmed by 1H NMR spectroscopy and gas chromatography-mass spectrometry. The NMR spectra were recorded on a Bruker DRX-400 and a Bruker AVANCE-500 spectrometers. The mass spectra were obtained on a Shimadzu GCMS-QP2010 Ultra instrument. The 1H NMR spectra of obtained dipyrimidines contained no singlets of the pyrimidine ring characteristic for the 5-H proton at δ 4.90-5.05 ppm, but they contained the signals of the CHPh proton at δ 5.35-5.50 ppm. The monosubstituted phenyl ring had signals at δ 7.00-7.25 ppm, while the protons of di- and trisubstituted phenyl ring characteristically appeared in a higher field at δ 6.55-6.90 ppm and 6.60-6.70 ppm, respectively. The characteristic features of all analyzed mass spectra were the molecular ion peak, as well as the C5-CHPh bond rupture and formation of phenyl cation. The mass spectra of all studied compounds contained peaks, characteristic for fragmentation of initial 2-organylsulfanyl-6-aminopyrimidin-4(3 H )-ones. Interaction with aromatic aldehydes proceeded in two stages, which was proved by the formation of 6-amino-5-(hydroxy(phenyl)methyl)-2-methallylsulfanylpyrimidin-4(3 H )-one and 5,5'-(phenylmethylene) bis (2-methallylsulfanyl-6-aminopyrimidin-4(3 H )-one) mixture in the reaction of 2-methallylsulfanyl-6-aminopyrimidin-4(3 H )-one with benzaldehyde with equimolar ratio. All attempts to obtain the tricyclic system, namely, substituted pyrido[2,3- d :6,5- d ’] dipyrimidines by the intermolecular elimination of the ammonia molecule were unsuccessful. The reaction of 5,5'-(phenylmethylene) bis (2-allylsulfanyl-6-aminopyrimidin-4(3 H )-one with iodine led to formation of 6,6'-(phenylmethylene) bis (5-amino-3-(iodomethyl)-7-oxo-2,3,7,8-tetrahydrothiazolo[3,2- a ]pyrimidinium) iodide, as proved by 1H NMR. The 1H NMR spectrum contained the characteristic signal of the NCH+ proton at δ 5.29 ppm.