INTRAMOLECULAR SULFENYLATION USING SULFOXIDES - PREPARATION OF 5H-PYRROLO[1,2-A][3,1]BENZOTHIAZINES

N-[2-(Phenylsulfinylmethyl)phenyl]pyrrole (4) undergoes transfer sulfenylation to N-(2-chloromethylphenyl)-2-phenylthiopyrrole (5') presumably via S-phenyl 5H-pyrrolo[1,2-a][3,1]benzothiazonium chloride (7). Depending upon the rigor of the reaction conditions, either N-(2-hydroxymethylphenyl)-2-phenylthiopyrrole (5) or its 5-trifluoroacetyl derivative (6) are obtained when 4 is treated with TFAA in trifluoroacetic acid. N-[2(Methylsulfinylmethyl) aryl]pyrroles (12), when treated with gaseous hydrogen chloride and the resulting sulfonium salts refluxed in dichloroethane, produce substituted 5H-pyrrolo[1,2-a][3,I]benzothiazines (14). 1-Formyl-5H-pyrrolo[1,2-a][3,1]benzothiazines (22) are formed in one step in good yield when sulfoxides (12) are reacted with the Vilsmeier-Haack reagent (DMF/POCl3). No Pummerer rearrangement product is isolated from these reactions.