An efficient synthesis of 3‐aminoisothiazolo[5,4‐<i>b</i>] ‐quinoline from quinoline

Abstract

Abstract Treatment of readily available 3‐formylquinoline‐2‐thiol ( 1 ) with ammoniacal sodium hypochlorite directly afforded isothiazolo[5,4‐ 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‐aminoisothiazolo[5,4‐ b ]quinoline ( 7 ).