Access to [2,1]Benzothiazine S,S‑Dioxides from β‑Substituted o‑Nitrostyrenes and Sulfur

[2,1]­Benzothiazine S,S-dioxides 2 were synthesized by simply heating o-nitrostyrenes with elemental sulfur in 3-picoline with complete atom economy. This reaction was found to occur without any added catalyst and consist of a cascade of reduction of the nitro group, sulfuration of a C–H of the double bond, oxidation of a sulfur atom to its highest oxidation state by the migration of two oxygen atoms from the nitro group, and formation of new N–S bonds. Furthermore, the method could also be applied to o-nitrocinnamamides and cinnamate esters.