= Solution
Sulfuryl chloride converts the aryl thiol into an electrophilic sulfur reagent, conveniently represented as $\mathrm{ArSCl}$ after chlorination and dehydrogenation. Triethylamine traps the generated acid. The pyrrole's two $\alpha$ positions are already occupied; its less deactivated remaining carbon, C4, attacks electrophilic sulfur, displacing chloride. Loss of the C4 proton restores the aromatic ring and gives the \b[C4 arylthio-substituted pyrrole].
The net new bond is C(pyrrole)–S(aryl). Sulfur is retained from the thiol and becomes a thioether; the transformation is not sulfonylation by transfer of sulfuryl chloride's SO$_2$ group. Possible disulfide formation during thiol chlorination does not change the electrophilic-sulfenylation logic of the final ring substitution.
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