Aromatic Ring-Opening of 2-Fluorobenzothiophenes by Alkyllithiums

Diphenylacetylenes are obtained when alkyllithium ­reagents are added to 3-aryl-2-fluorobenzothiophenes at low temperature. The aromatic ring-opening mechanism involves a nucleophilic addition of the alkyllithium to the sulfur atom of the thiophene. The resulting 2,2-diaryl-1-fluorovinyl anion subsequently undergoes a Fritsch-Buttenburg-Wiechell rearrangement to ­afford the diphenylacetylene.