Figure 2. Mechanism of regioselective metal-free C3 C–H functionalization of benzothiophene S-oxides.

Activated benzothiophene S-oxides III capture nucleophilic coupling partners prior to regioselective delivery to C3 via a charge accelerated [3,3]-sigmatropic rearrangement of intermediates I and II. The expected products of direct addition of nucleophiles to III, the para-substituted phenols 11, alkenes 12 and allenes 13, were not observed. Nu, nucleophile.