[4+2] cycloaddition reactions between 2,4-diamino-1-thia-3-azabutadienes and ketene. Synthesis of new 1,3-thiazin-6-ones, 1,3-thiazine-6-thiones and 2-thioxopyrimidin-4-ones

The reaction of 2,4-diamino-1-thia-3-azabutadienes with an excess of ketene afforded 2-amino-1,3-thiazin-6-ones and 2-thioxopyrimidin-4-ones by [4+2] cycloaddition reaction. Reaction between thiazabutadienes and ketene gave r ise to aminothiazinones, which were sulfured by action of phosphorus pentas ulfide leading to aminothiazinethiones. Furthermore, synthesis of thioxopyr imidinones starting from S-methyl salts of thiazadienes is described.