New Syntheses of Benzo[b][1,4]thiazines

1,4-Benzothiazine derivatives have been extensively studied because of their biological activities including anti-fungal, anti-tumor, anti-HIV and KATP-channel opener properties. These different effects indicate the 1,4-benzothiazine as a useful target skeleton in organic and medicinal chemistry research. In this communication we describe two novel approaches to the preparation of benzo[b][1,4]thiazines. Depending upon the nature of the starting aniline the final heterocycles can be obtained via a hetero Diels-Alder reaction of a transient o-iminothioquinone or reacting N-protected o-anilinodisulfides with styrenes in the presence of a Cu(II) catalyst. The mechanisms related with both processes will be discussed in detail.