Regiodivergent Photocatalytic Annulation for the Synthesis of gem-Difluorinated Cyclic Hydrocarbons.

Regiodivergent synthesis is a powerful strategy for expanding chemical space. Given the significance of fluorine-containing molecules in pharmaceutical sciences, a regiodivergent [3+2] cycloaddition of gem-difluorocyclopropyl urea to olefins and [1.1.0]-bicyclobutanes was developed by employing cationic iridium complexes as photocatalysts under visible-light irradiation. By properly selecting a counteranion of the photocatalyst and tuning the reaction conditions, each regioisomeric cyclic hydrocarbon with a defined gem-difluoromethylene disposition was directly assembled with high selectivity. Mechanistic elucidation revealed the critical relevance of the basicity of the photocatalyst counteranion to the regiochemical outcome. The reaction diverges depending on the intervention of deprotonation of the initially generated urea radical cation by the pairing anion to form the corresponding neutral radical; this not only governs the regioselective ring opening of the cyclopropane moiety but also modulates the relative reactivity of the two resulting terminal carbon radicals, thereby dictating the dominant pathway.