Heteroanalogs of alloxazines

The properties of derivatives of 6,8-dimethyl-7,9-dioxo-5H-6,7,8,9-tetrahydropyrimido[4,5-b][4,5-e][1,4]thiazines have been investigated. These substances are stable in the crystalline form and are readily oxidized in moist solutions in chloroform or methylene chloride, being converted to 9a-hydroxy derivatives. In the example of the 4-dimethylamino derivative, a stagewise mechanism has been shown for the process of one-electron oxidation of the thiazines, proceeding through the formation of a free-radical structure. The thiazinyl radicals have been found to be capable of one-electron redox reactions. A tendency of the thiazines to form 9a-derivatives has been noted.