A novel cyclization reaction of o-carboxyphenyl and o-carbamoylphenyl sulfoxides. Formation of benzoxathiane, dihydrobenzothiazine and benzoisothiazoline derivatives

Article abstract of DOI:10.1016/S0040-4020(01)97423-X

When o-carboxyphenyl or o-carbamoylphenyl sulfoxide was heated with a large excess of acetic anhydride at 100-130° for 1-3 h, 6-membered heterocyclic compounds, i.e., 3,1 - benzoxathian-4 - one and 2,3 - dihydro - 1,3 - benzothiazin - 4 - one, and a 5-membered heterocyclic compound, i.e., 1,2-benzoisothiazolin-3-one were obtained in good yield. Cyclization would take place by the initial intramolecular nucleophilic attack of either the sulfinyl O atom at ortho-carbonyl carbon or the N atom of the amide group at ortho-sulfinyl S atom to give a 5-membered cyclic acyloxysulfonium salt or aminosulfonium salt, which undergoes an intramolecular Pummerer rearrangement to afford the heterocyclic compounds.