Access to [2,1]Benzothiazine ,-Dioxides from β-Substituted -Nitrostyrenes and Sulfur.

[2,1]Benzothiazine ,-dioxides were synthesized by simply heating -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 -nitrocinnamamides and cinnamate esters.