Carbonylation and Other Transformations of Polyfluorobenzocyclobutenols in Superacids

Acid-catalyzed carbonylation of a series of polyfluorinated benzocyclobuten-1-ols, as well as cyclic sulfuric acid esters derived from benzocyclobutene-1,2-diols, with carbon monoxide in the presence of TfOH and FSO₃H–SbF₅ gave both CO addition products with retention of the four-membered ring (the corresponding carboxylic acids) and carbonylation products. In the latter case, the reaction was accompanied by ring opening, ring opening with subsequent heterocyclization to isochroman derivatives, and ring expansion to five-membered cycle. Polycyclic dimeric products were also formed in some cases.