Ring transformation of 1,1-dioxo-1,2-thiazine-6-carbaldehydes with nitrogen nucleophiles to substituted pyridine-3-sulfonanilides

Article abstract of DOI:10.1055/s-1996-4382

1,1-Dioxo-1,2-thiazine-6-carbaldehydes 1 possessing a masked 1,5-dicarbonyl structure react with hydroxylamine with ring transformation to form the pyridine N-oxides 2. These can be deoxygenated with PCl₃ to give the corresponding pyridine-3-sulfonanilides 3, which are available by the reaction of 1 with ammonia as well. The ring transformation of 1 with methylamine, benzylamine and hydrazine produces N-substituted mesoionic pyridinium salts 6-8. The cyclohexane-fused thiazine-6-carbaldehyde 9 can be transformed with ammonia to the 5,6,7,8-tetrahydroquinoline 10. Reaction of 2 with NaNO₂/HCl enables the introduction of the nitro group into the anilide part of the molecule.