抄録
The product distributions resulting from methylation of 3-phenyl-1, 2, 4-triazolin-5-one (1a) and 3-phenyl-1, 2, 4-triazoline-5-thione (1b) and their monomethylated derivatives (2a, b-5a, b) with methyl iodide and diazomethane in various solvents were studied by nuclear magnetic resonance spectroscopy. The methylations of 1-methyl-3-phenyl-1, 2, 4-triazolin-5-one (3a), 5-hydroxy-2-methyl-3-phenyl-1, 2, 4-triazole (4a), and 4-methyl-3-phenyl-1, 2, 4-triazolin-5-one (5a), with methyl iodide in alkaline solution occurred preferentially at the N-atoms and afforded mainly 1, 4-dimethyl-3-phenyl-1, 2, 4-triazolin-5-one (9a), mesoionic anhydro-2, 4-dimethyl-5-hydroxy-3-phenyl-1, 2, 4-triazolium hydroxide (11a), and 9a, respectively. The product ratios on methylations of 3a, 4a, and 5a with diazomethane were affected variously by the type of solvent, the nucleophilicities of the four reaction sites, and the steric factor. Dimethyl sulfoxide (DMSO) increased O-methylation in all cases and especially with 4a, which exists in the OH form, methylation occurred almost exclusively at the oxygen atom in DMSO. The methylations of 1b and its N-methylated derivatives (3b-5b) with either methyl iodide or diazomethane gave S-methylated products predominantly in all the solvents used.
