N-Substituted isothiazol-3(2H)-ones can be easily prepared fromN-substituted 3-benzoylpropi-onamides in two experimentally simple steps, in satisfactory overall yields. Reaction of the amides with excess thionylchloride results in the formation of N-substituted 5-benzoylisothiazol-3(2H)-ones, which are readily debenzoylated with alkali to the corresponding N-substituted isothiazol-3(2H)-ones. This