Simple pyrimidines. Part X. The formation and reactivity of 2-, 4-, and 5-pyrimidinyl sulphones and sulphoxides

Abstract

The hitherto unknown sulphones (2-, 4-, and 5-methylsulphonyl- and 2-phenylsulphonyl-pyrimidine) and sulphoxides (2-, 4-, and 5-methylsulphinyl- and 2-phenylsulphinyl-pyrimidine) are prepared from the corresponding thioethers by oxidative methods. 2-Phenylsulphonylpyrimidine is also made from 2-chloropyrimidine with sodium benzenesulphinate. The 2- and 4-derivatives undergo a variety of ready nucleophilic displacement reactions on a preparative scale, and second-order rate constants for their aminolysis by pentylamine or cyclohexylamine in dimethyl sulphoxide are reported. These figures indicate that the sulphones and sulphoxides are a little more reactive than the corresponding chloropyrimidines, and >10⁵-times as reactive as the thioethers from which they are derived. Both 2-sulphones undergo an unprecedented reduction by hydriodic acid to 2-methyl (or phenyl) thiopyrimidine. The base-weakening effect of sulphonyl or sulphinyl substituents on pyrimidine is marked in the 2- and 4-derivatives but minimal in the 5-isomers.