The chemistry of 2,1-benzisothiazoles. Part VII. Reaction of α-substituted o-toluidines with thionyl chloride. A one-stage synthesis of 2,1-benzisothiazole-3-carboxylic acid

Abstract

o-Benzylaniline (II; R = Ph) affords a quantitative yield of 3-phenyl-2,1-benzisothiazole (III; R = Ph) when heated with thionyl chloride, but o-toluidines functionally substituted at the methyl group (II; R = CN, OH, or Cl) give only N-sulphinyl derivatives or tars. o-Ethylaniline (II; R = Me) probably affords 3-methyl-2,1-benziso-thiazole (III; R = Me) as an intermediate, but the latter is rapidly chlorinated at the methyl group, and after hydrolysis 2,1-benzisothiazole-3-carboxylic acid (III; R = CO₂H) is obtained in 30% yield. More highly substituted o-alkylanilines produce N-sulphinylamines, only traces of 2,1-benzisothiazoles being formed.