Rhodium-Catalyzed Oxidative Aimulation of Sulfoximines and Alkynes as an Approach to 1,2-Benzothiazines

摘要

Within the last few years, oxidative activation reactions of C— H/N—H or C-H/O—H bond combinations with subsequent alkyne or alkene annulations have become the synthetically most useful C—C and C—X (X = N, O, etc.) bond-forming processes. Various metals proved applicable, and complexes based on Pd~(II), Rh~(III), or Ru~(II) have been utilized for the catalytic construction of a wide range of heterocycles. To the best of our knowledge, 1,2-benzothiazines have not been among the heterocyclic products, despite their usefulness as scaffolds in drug development and as synthetic intermediates. Harmata and co-workers have introduced the most advanced approaches towards 1,2-benzothiazines, including annulations of sulfonimidoyl chlorides with alkynes or alkenes, palladium catalysis in domino reaction sequences starting with a Buchwald-Hartwig N-arylation, and Sono-gashira-type cross-coupling reactions of S-2-bromophenyl-S-methylsulfoximines with terminal alkynes [Eq. (1); DMF = N,N-dimethylformamide] . None of these 1,2-benzothiazine syntheses involve the oxidative C—H/N—H activation of simple alkyl aryl sulfoximines.