Sulfoxide electrophilic sulfenylation ( SES ) is a useful technique for heterocyclic synthesis (eqn. 1). We have exploited pyrrole-containing sulfoxides for intramolecular sulfenylation to form a wide variety of N,S- heterocycles. [1]

This general reaction, which takes place under traditional Pummerer rearrangement reaction conditions (TFAA), produces sulfenylation products cleanly in good to excellent yields when R is a simple alkyl group (R = CH3, C2H5). This process is thought to proceed via a mechanism similar to the Pummerer rearrangement. [2] except that nucleophilic attack occurs at sulfur before the elimination reaction to a thionium ion for the Pummerer rearrangement pathway takes place (eqn. 2). In all cases we have examined to date, the nucleophilic source has been the pi-electron rich pyrrole ring, tethered in some fashion to the sulfoxide moiety.

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