NITROSATION OF 2-ARYL-3,5-DIMETHYL-1,1-DI OXO-1,2-THIAZINES - AN UNUSUAL RINGTRANSFORMATION TO MESOIONIC PYRIDAZINIUM SALTS

The thiazines 1b-e, g, h react with isoamyl nitrite/HClg by nitrosatio n of the 3-methyl group to the 3-cyano-thiazines 3b-e, g, h. As by-pro ducts the mesoionic pyridazinium salts 4b, c are formed. The compounds 4b-i and 4-1e-i became main products by the nitrosation of 1b-i with sodium nitrite/HCl. In this case as by-products the oximes 2b-d were i solated, which can be transferred with sodium nitrite into 4b-d, The r egioselectivity of the nitrosation reaction of 1 is influenced by the substituents of the aryl group.