Synthesis of C2 Substituted Benzothiophenes via an Interrupted Pummerer/[3,3]‐Sigmatropic/1,2‐Migration Cascade of Benzothiophene S‐Oxides

Functionalized benzothiophenes are important scaffolds found in molecules with wide ranging biological activity and in organic materials. We describe an efficient, metal‐free synthesis of C2 arylated, allylated, and propargylated benzothiophenes. The reaction utilizes synthetically unexplored yet readily accessible benzothiophene S‐oxides and phenols, allyl‐, or propargyl silanes in a unique cascade sequence. An interrupted Pummerer reaction between benzothiophene S‐oxides and the coupling partners yields sulfonium salts that lack aromaticity and therefore allow facile [3,3]‐sigmatropic rearrangement. The subsequently generated benzothiophenium salts undergo a previously unexplored 1,2‐migration to access C2 functionalized benzothiophenes.