An efficient synthesis of 3-aminoisothiazolo[5,4-b] -quinoline from quinoline

Treatment of readily available 3-formylquinoline-2-thiol ( 1 ) with ammoniacal sodium hypochlorite directly afforded isothiazolo5,4-b]quinoline ( 3 ) in high yield, probably via 3-formylquinoline-2-sulfenamide ( 2 ). Facile conversion of 3 to the corresponding 3-amino derivative ( 7 ) was accomplished by the following sequence: base induced opening of the isothiazole ring to 3-cyanoquinoline-2-thiol ( 5 ), oxidation of 5 to the corresponding stable sulfenamide ( 6 ) and sodium ethoxide catalysed reclosure of the isothiazole ring which provided 3-aminoisothiazolo5,4-b]quinoline ( 7 ).