HETEROCYCLIC SYNTHESIS WITH 3-CYANO-2(1H)PYRIDINETHIONE - SYNTHESIS OF 3-OXO-2,3-DIHYDROISOTHIAZOLO[5,4-B]PYRIDINE AND RELATED-COMPOUNDS

3-Carbethoxy-4,6-diphenyl-2-pyrridine sulfonamide (5), can be cyclized to 3-oxo-2,3-dihydro-4,6-diphenylisothiazolo[5,4-b]pyridine-1,1-dioxide (2). Oxidation of pyridinethione 6 with Cl2/H2O gave the sulfonyl chloride derivative 7, which can be ammonolyzed to 3-amino-4,6-diphenylisothiazolo[5,4-b]pyridine-1,1-dioxide (8), and 3-cyano-4,6-diphenylpyridine-2-sulfonamide (9). Hydrolysis of 6 gave 3-carboxamido-2(1 H)pyridinethione (12) which can be oxidized with iodine to 3-oxo-4,6-diphenyl-2,3-dihydroisothiazolo[5,4-b]pyridine (13). 3-Methyl-4,6-diphenylisothiazolo[5,4-b]pyridine-1,1-dioxide (17) was also prepared from 6. © 1990 Springer-Verlag.