Ketone–olefin coupling reactions are common methods for the formation of carbon–carbon bonds. This reaction class typically requires stoichiometric or super stoichiometric quantities of metal reductants, and catalytic variations are limited in application. Photoredox catalysis has offered an alternative method toward ketone–olefin coupling reactions, although most methods are limited in scope to easily reducible aromatic carbonyl compounds. Herein, we describe a mild, metal-free ketone–olefin coupling reaction using an excited-state acridine radical super reductant as a photoredox catalyst. We demonstrate both intramolecular and intermolecular ketone–olefin couplings of aliphatic and aromatic ketones and aldehydes. Mechanistic evidence is also presented supporting an “olefin first” ketone–olefin coupling mechanism.

The photocatalytic C–F functionalization of highly fluorinated arenes is a powerful method for accessing functionalized multifluorinated arenes. The decisive step in the determining regioselectivity in fluorine functionalization is fluoride fragmentation from the radical anion of the multifluorinated arene. To date, the availability of regioisomers has been dictated by the innate electronics of the fluorinated arene, limiting the synthetic utility of the chemistry. This study investigates the remarkable ability of a strategically located hydrogen bond to transcend the normal regioselectivity of the C–F functionalization event. A significant rate acceleration is additionally observed for hydrodefluorination of fluorines that can undergo intramolecular hydrogen bonds that form 5–8 membered cycles with moderately acidic N–Hs. The hydrogen bond is expected to facilitate the fragmentation not only by bending the C–F bond of the radical anion out of planarity, but also by increasing the exothermicity of the fluoride extrusion step through protonation of the naked fluoride. Finally, the synthetic utility of the method is demonstrated in an expedited synthesis of the trifluorinated α-phenyl acetic acid derivative required for the commercial synthesis of Januvia, an anti-diabetic drug. This represents the first synthesis of a commercially important multifluorinated arene via a defluorination strategy, and is significantly shorter than the current strategy.

No abstract

Metrics & More Article RecommendationsA s of April 8, 2020, the authors have issued an Expression of Concern to alert readers that some of the spectra in the Supporting Information may have been digitally modified. An investigation is currently underway, and the status of this Article will be updated following completion of this investigation.