Isothiazoles. Part V. Cycloaddition reaction of nitrile oxides to 3-diethylamino-4-(4-methoxyphenyl)-isothiazole 1,1-dioxide: An entry to 5-acyl- and 5-cyano-isothiazole 1,1-dioxide derivatives

Nitrile oxides 2 reacted with 3-diethylamino-4-(4-methoxyphenyl)-isothiazole 1,1-dioxide (1) affording through a highly regioselective 1,3-dipolar cycloaddition reaction isothiazolo[5,4-d]isoxazoline 4,4-dioxides 3. Reduction of 3 afforded a mixture of the E and Z forms of the corresponding 5-(amino-aryl-methylene)-dihydro-isothiazole 1,1-dioxides 4/5 which were transformed into 5-acyl-dihydro-isothiazole 1,1-dioxides 6 and the corresponding dehydrated products 7. Compound 3f was easily transformed into 5-cyano-isothiazole 1,1-dioxide 11.