Pyridine N-sulfides. Benzisothiazolo[2,3-a]pyridinium tetrafluoroborates and benzothiopheno[3,2-b]pyridines. Novel heterocyclic systems

2-(2-Mercaptophenyl)pyridines are prepared from the corresponding phenols and oxidized with N-chloro-succinimide and silver tetrafluoroborate to benzisothiazolo[2,3-a]pyridine salts ( 4 ). The latter do not rearrange thermally or photochemically to benzothiopheno[3,2-b)pyridines ( 19 ) and are attacked by nucleophiles at sulfur rather than in the pyridine ring, to give the original 2-(2-mercaptophenyl)pyridine back in a reaction involving a dismutation. 19 is prepared by rearranging O-[2-(3-bromo-2-pyridyl)-4-nitrophenyl]dimethylthio-carbamate to the S-aryl compound and heating the latter with strong base.