A novel photoisomerzation of 1,2-benzothiazine 1,1-dioxides to 1,3-benzothiazine 1,1-dioxides

A novel facile photoconversion of 4-hydroxy-1,2-bezothiazine 1,1-dioxides (3a-e) into 4-oxo-1,3-2H-benzothiazine 1,1-dioxides (4a-e) and 4-hydroxy-2-methyl-N-(pyridin-2-yl)-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide (PRX) into N-methyl saccharin (2) upon 254 nm irradiation in methanol or acetonitrile is reported. The structures of the products have been elucidated by spectroscopic methods and single crystal X-ray structure determination for 4a and 4d.