Dihydrobenzothiazine dioxides

Irradiation of the / -(aryl)ethanesulfonamides 190 in the presence of DAIB-I2 provides access to the dihydrobenzothiazine dioxides 191 and 192 (Scheme 55) (OOJOC926). In these reactions, formation of the thiazine ring by the radical cyclization pathway to give 191 is followed by electrophilic iodination of the arene nucleus to give 192. 

Benzo>l,2-thiazines.—Syntheses of new 1,2-benzothiazines of pharmacological interest continue to attract most of the attention in this area. Sianesi et aL now report some convenient procedures for preparing the three isomeric dihydrobenzothiazine dioxides (9)—(11) and their N-substi-tution products. For instance, (10) is obtained in 54% yield by dehydration of o-(2-aminoethyl)benzenesulphonic acid with POCI3, and also by hydrogenation in acidic medium of the corresponding cyanosulphonamide (77% yield) or by alkaline treatment of o-(2-chloroethyl)benzenesulphonamide (83% yield). Several 3,4-dihydro-l/f-2,3-benzothiazin-4-one 2,2-dioxides and 3,4-dihydro-177-l,2-benzothiazin-4-one 2,2-dioxides, as well as 3,4-... 

Many ortho substituted-benzenesulfonylureas have recently been commercialized as herbicides. This discovery initiated a program to incorporate the ortho group of the benzenesulfonamide into a second ring, forming a bicyclic sulfonamide. The synthesis of a variety of bicyclic arylsulfonamides, such as, dihydrotenzothiophenes, benzothiopyrans, dihydroisocoumarins, dihydrobenzothiazine-dioxides, indanones and benzisothiazoles, is described. 

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