The benzothiazine nucleus is a relatively unexplored class of compounds, from the standpoint of both synthetic chemistry and biological activity. We have developed a rapid, high-yielding synthesis of benzothiazines in which a precursor aryl thiourea is prepared on solid phase. Addition of trifluoroacetic acid catalyzes a conjugate addition reaction to form the desired heterocycle and releases it from the resin.

A critically important strategy for synthetic chemistry is the development of "domino" processes: those capable of concatenating multiple transformations into a single step. Such transformations not only provide an increase in synthetic efficiency, but also imply the development of a significant degree of mechanistic understanding. We report herein a new domino reaction, in which a chromium-manganese redox couple is employed both to catalytically reduce an o-hydroxy nitroarene and to oxidatively cyclize a subsequently formed imine. We find that the reaction is most effective for starting o-hydroxy nitroarenes with a strongly electron-withdrawing group at the para position.

No abstract

A wide range of aromatic nitro compounds can be reduced to anilines through the use of a Cr(II)/Mn(0) redox couple in the presence of trimethylsilyl chloride [TMSCl, Eq. (1)]. Only 0.25 equivalents of chromium are required to reduce solid-supported nitroarenes (R=solid support); this represents a rare case of transfer catalysis between two solid phases. The reaction is also amenable to solution-phase synthesis (R=OH).

[structure: see text] We have developed an apparatus for carrying out redox-coupled chromium-manganese or chromium-zinc reactions on solid-supported substrates which allows recycling of the stoichiometric reductant. In addition to providing a greatly simplified procedure for these reactions, we observe striking differences in the recyclability of Mn and Zn. A preliminary extension of the methodology to the catalytic coupling of allylchromium reagents with solid-supported aldehydes is also reported.