Synthesis of Ring-Fluorinated Thiophene Derivatives Based on Single C-F Bond Activation of CF-Cyclopropanes: Sulfanylation and 5-- Cyclization.

The treatment of CF-bearing cyclopropanes with EtAlCl generated stabilized difluorocarbocations, which underwent a nucleophilic addition of thiocarboxylic acids or thiols. The sulfur functionality was introduced at the position δ to the fluorine substituents in a regioselective manner (single activation of CF-cyclopropanes). The formed 1,1-difluoro-1-alkenes underwent successive deesterification/5-- cyclization. Intramolecular vinylic substitution proceeded in an aprotic solvent, whereas intramolecular addition proceeded in a protic solvent to afford pharmaceutically and agrochemically promising 2-fluoro-4,5-dihydrothiophene and 2,2-difluorotetrahydrothiophene scaffolds, respectively.