Studies on 1,3-Benzoxazines. III. Reaction of Imidoyl Chlorides of 1,3-Benzoxazines with 2-Hydroxy- or 2-Mercaptopyridine N-Oxides : A Novel S-N Bond Formation via Electrocyclic Rearrangement

A novel S-N bond formation through 3, 3-sigmatropic rearrangement in the reaction of imidoyl chlorides of 1, 3-benzoxazines (1) with 2-mercaptopyridine N-oxide (8) is described. Treatment of the imidoyl chlorides (1a-f) with 2-hydroxypyridine N-oxide (2) afforded the corresponding pyridone derivatives (3a-f). When 2-mercaptopyridine N-oxide (8) was used instead of 2, the thiopyridones (7) or N-oxides (9) were obtained and both compounds were transformed to 3-(2-pyridylthio)-4-oxo-2, 3-dihydro-1, 3-benzoxazines (13) through electrocyclic rearrangement on heating in a suitable solvent.