Some reactions of 3-acetamido-2-nitrobenzo[b]thiophen and its 5-chloro- and 5-bromo- derivatives

Abstract

The oximes of 3-acetylbenzo[b]thiophen and its 5-chloro- and 5-bromo- derivative underwent the Beckmann rearrangement (80–90%). The resulting amides were nitrated to give (80%) the compounds mentioned in the title. On treatment with ferrous oxalate at 225°, each of these gave a mixture of the corresponding 3-cyano-1,2-benzisothiazole and its 3-carbonamide. 5-Chlorobenzo[b]thiophen-2,3-dione was prepared by a standard route from 5-chloro-3-hydroxybenzo[b]thiophen. On treatment with hydrogen peroxide and ammonia it gave 5-chloro-1,2-benzisothiazole-3-carbonamide, which was converted into the nitrile by heating with phosphorus pentoxide. 1,2-Benzisothiazole-3-carbonamide, and the corresponding nitrile, were similarly prepared from benzo[b]thiophen-2,3-dione. The resulting amides and nitriles were identical with those obtained from the ferrous oxalate reactions. 2,3-Diacetamidobenzo[b]thiophen was prepared by the catalytic reduction of 3-acetamido-2-nitrobenzo[b]thiophen, and acetylation of the resulting unstable amine. It was converted into an imidazole derivative by boiling with dilute hydrochloric acid.