Intramolecular capture of pummerer rearrangement intermediates. I. Synthesis of pyrrolo[2,1-c][1,4]benzothiazines

Treatment of 1-(2-alkylsulfinylphenyl)pyrroles with trifluoroacetic acid in refluxing toluene gives 4-substituted pyrrolo[2,1-c][1,4]benzothiazines in good yield when the alkyl group bears an electron withdrawing substituent on the α-carbon. In the absence of such a group, starting material is recovered. The sulfoxides are prepared by oxidation (mCBPA) of the corresponding sulfide. The sulfides are prepared from 2-aminobenzenethiol either by S-alkylation followed by conversion to the pyrrole using 1,4-dimethoxytetrahydrofuran in glacial acetic acid or by S-alkylation of 1-(2-phenylmercapto)pyrrole followed by oxidation to the sulfoxide.