Convenient synthesis of 1,2-benzisothiazol-3(2H)-ones by cyclization reaction of acyl azide

1,2-Benzisothiazol-3(2H)-one was synthesized by treatment of 2-mercaptobenz oic acid with diphenyl phosphoryl azide, followed by cyclization of the res ulting acyl azide at low temperature, where Curtius rearrangement did not o ccur. 5-Amino-1,2-benzisothiazol-3(2H)-one was similarly synthesized in one pot from 4-mercaptoisophthalic acid.