Thiophenes 1 were treated with m-chloroperbenzoic acid (m-CPBA) under BF3⊙ Et2O catalysis to afford thiophene S-monoxides. These could be reacted in situ as intermediary species with a number of dienophiles to provide arenes (with alkynes as dienophiles) or 7- thiabicyclo [2.2. 1] hept-2-ene 7-oxides (with alkenes as dienophiles). It was also possible to isolate thiophene S-monoxides in solution and to cycloadd them in a second step. In ...
