Mesoionic dimethyl derivatives of some 1,2,4-triazinones. The course of the reaction of 3,5-dimethoxy, 3-methoxy-5-methylthio, 5-methoxy-3-methylthio and 3,5-bis(methylthio)-1,2,4-triazine with methyl iodide

Article abstract of DOI:10.1002/jhet.5570300523

Treatment of 3,5-dimethoxy-1,2,4-triazine (1a) with methyl iodide was found to give depending on the reaction time triazinium iodide 2a, triaziniumolates 4a and 6a as well as methoxytriazinones 7a and 8a. Thermolysis of 2a gave triaziniumolates 4a and 6a. Reaction of 2a, 4a or methoxytriazinone 9a with methyl iodide in acetonitrile yielded as the sole product 6a. Reaction of 3-methoxy-5-methylthio-1,2,4-triazine (1b) with methyl iodide gave triazinium iodide 2b and methylthio triazinone 7b. Hydrolysis of 2a,b afforded 4a. Reaction of 5-methoxy-3-methylthio-1,2,4- triazine (1c) with methyl iodide gave triazinium iodide 2c, triaziniumolate 4b, triazinium iodide 5b and triazinone 8b. Hydrolysis of 2c yielded 4b and its thermolysis gave a mixture of 4b and 5b. Reaction of 2c, 4b and triazinone 9b with methyl iodide afforded 5b. Treatment of 3,5- bis(methylthio)-1,2,4-triazine (1d) with methyl iodide was found to give a mixture of N1 and N2 methiodides 2d and 3d which gave on hydrolysis 4b and 8b, respectively. Methylation of 6-methyl derivatives 1e-g gave analogous results, however the proportions of N1 methylated products were lower and the reaction rates higher in comparison to their respective lower homologues 1a,c,d. The structures of the mesoionic dimethyl derivatives were assigned from uv, ir, ¹H nmr and electron impact mass spectra. The structural assignments were eventually confirmed by quantum chemical calculations of net charge distributions, bond lengths and ipso angles of the C5-O bonds.