Pyrrolylsulfonium salts: stable, accessible and versatile pseudohalides for Stille couplings

Abstract

Pyrrolyl halides can be difficult to synthesise in a regioselective manner and are often unstable, which has hampered their application in cross-coupling. Here we introduce pyrrolylsulfonium salts as advantageous pseudohalide coupling partners and showcase their applicability in Stille couplings. Benefits of these salts include their straightforward synthesis via an “interrupted Pummerer” process, their high stability, and the ability to selectively introduce the sulfonium group at either the pyrrole α- or β- position as required. The Stille coupling has been demonstrated for aryl, heteroaryl and alkynylstannanes, and the effect of the pyrrole substituents on the regioselectivity of S–C bond activation has been investigated. Conditions to effect N-desulfonylation of N-trisyl coupling products have been identified.