1,2,4‐benzothiadiazine 1,1‐dioxides 3. Reactions of 2‐aminobenzenesulfonamide with chloroalkyl isocyanates

Reactions of 2‐aminobenzenesulfonamide ( 1 ) with allyl, methyl, 2‐chloroethyl aor 3‐chloropropyl isocyanates gave 2‐(methylureido)‐, 2‐(allylureido)‐, 2‐(2′‐chloroethylureido)‐ and 2‐(3′‐chloropropylureido)‐benzene sulfonamides 3a,b and 7a,b in excellent yields. Treatment of 3a,b at refluxing temperature of DMF afforded 2 H ‐1,2,4‐benzothiadiazin‐3(4 H )‐one 1,1‐dioxide ( 4 ) in good yield. However, when compounds 7a,b were refluxed in 2‐propanol, 3‐(2′‐aminoethoxy)‐2 H ‐1,2,4‐benzothiadiazine 1,1‐dioxide ( 11a ) and 3‐(3′‐aminopropoxy)‐2 H ‐1,2,4‐benzothiadiazine 1,1‐dioxide ( 11b ) were obtained in a form of the hydrochloride salts 10a,b in 87% and 78% yields respectively. Heating 11b in ethanol gave a dimeric form of 2 H ‐1,2,4‐benzothiadiazin‐3(4 H )‐one 1,1‐dioxide and 3‐(3′‐aminopropoxy)‐2 H ‐1,2,4‐benzothiadiazine 1,1‐dioxide ( 12 ) in 55% yield. Treating of 7a,b or 11a,b with triethylamine at the refluxing temperature of 2‐propanol afforded 3‐(2′‐hydroxyethylamino)‐2 H ‐1,2,4‐benzothiadiazine 1,1‐dioxide ( 2a ) and 3‐(3′‐hydroxypropylamine)‐2 H ‐1,2,4‐benzothiadiazine 1,1‐dioxide ( 2b ) via a Smiles rearrangement.