AbstractThe reactions of saccharin derivatives 1 with sodium alkoxides were studied. Under mild conditions, compounds 1a‐f gave the corresponding open sulfonamides 5a‐f. Under drastic conditions, β‐(saccharin‐2)propionic acid derivatives 1a,b reacted with sodium ethoxide affording saccharin and β‐ethoxypropionic acid derivatives 4a,b. γ‐(Saccharin‐2)butyric acid derivatives 1c,d and γ‐(saccharin‐2)‐butyrophenone 1f reacted with sodium t‐butoxide in dimethyl sulfoxide affording 5‐substituted 6‐hydroxy‐3,4‐dihydro‐2H‐1,2‐benzothiazocine 1,1‐dioxides 9. From mother liquors, 1‐substituted 2,3‐dihydro‐pyrrolo[1,2‐b][1,2]benzisothiazole 5,5‐dioxides 10 were isolated several hours later, though not detected immediately after completing the reaction. When the reactions were carried out in t‐butyl alcohol, the yields of 9 diminished and those of 10 increased with product ratio inversion. Different experimental observations on the possible pathway generating 9 and 10 are discussed.