REACTION OF BISVINAMIDINIUM SALTS OF 1,1- DIOXO-1,2-THIAZINE-6-ALDEHYDES WITH HYDROXYLAMINE TO SUBSTITUTED PYRIDO[4,3-E]-1,2-THIAZINE-1,1-DIOXIDES

The formylation of 2-aryl-3,5-dimethyl-1,1-dioxo-1,2-thiazines with PO Cl3/DMF leads to the thiazine-6-aldehydes 1 and to the bis-vinamidiniu m salts 2. The reaction of 2a,b with hydroxylamine results in the form ation of the pyrido-thiazine-N-oxides 5a,b, which give with PCl3 the 5 -cyano-3-isoxazol-4-yl-pyrido[4,3-e]thiazines 6a,b. The pyrido-thiazin es 9a and 10a are obtained by base-induced opening of the isoxazolyl-r ing in 5a and 7a to the cyanoformylmethyl group. The compounds 6a and 7a were characterized by Xray structure analysis.