Aerobic Oxidative EDA Catalysis: Synthesis of Tetrahydroquinolines Using an Organocatalytic EDA Active Acceptor

Abstract

A catalytic electron donor–acceptor (EDA) complex for the visible-light-driven annulation reaction between activated alkenes and N,N-substituted dialkyl anilines is reported. The key photoactive complex is formed in situ between dialkylated anilines as donors and 1,2-dibenzoylethylene as a catalytic acceptor. The catalytic acceptor is regenerated by aerobic oxidation. Investigations into the mechanism are provided, revealing a rare example of a catalytic acceptor in photoactive EDA complexes that can give access to selective functionalization of aromatic amines under mild photochemical conditions.

Recent Advances in Employing Catalytic Donors and Acceptors in Electron Donor–Acceptor Complex Photochemistry

“…Another recent example of a catalytic acceptor being employed in EDA complex formation was reported by Sundén and co-workers for the visible-light annulation between activated alkenes and N , N -dialkylanilines . The key photoactive EDA complex was formed in situ between N , N -dialkylanilines as the donors and 1,2-dibenzoylethylene as the catalytic acceptor.…”

“…Another recent example of a catalytic acceptor being employed in EDA complex formation was reported by Sundeń and co-workers for the visible-light annulation between activated alkenes and N,N-dialkylanilines. 68 The key photoactive EDA complex was formed in situ between N,N-dialkylanilines as the donors and 1,2-dibenzoylethylene as the catalytic acceptor. While UV−vis studies did support the formation of an EDA complex, the authors could not rule out an alternative mechanism where 1,2-dibenzoylethylene is directly excited and acts as a photosensitizer, as 1,2-dibenzoylethylene was also found to absorb in the visible region in the absence of amines.…”

Overcoming Back Electron Transfer in the Electron Donor–Acceptor Complex-Mediated Visible Light-Driven Generation of α-Aminoalkyl Radicals from Secondary Anilines

“…Synthesis of maleimides has been described elsewhere. 19 Purifications were performed using an automated column chromatography Biotage Isolera Spektra One with a Biotage SNAP-10 g KP-silica column together with a 1 g sample cartridge using n-heptane or petroleum ether (40−60 °C)/ ethyl acetate as the solvent mixture unless otherwise noted. 1 H (400 MHz) and 13 C (101 MHz) NMR spectra were acquired on an Agilent NMR machine at 25 °C.…”

“…All reagents and solvents were purchased from Sigma-Aldrich and Alfa Aesar and used without any further purification unless specified. Synthesis of maleimides has been described elsewhere . Purifications were performed using an automated column chromatography Biotage Isolera Spektra One with a Biotage SNAP-10 g KP-silica column together with a 1 g sample cartridge using n -heptane or petroleum ether (40–60 °C)/ethyl acetate as the solvent mixture unless otherwise noted.…”

Tetrachlorophthalimides as Organocatalytic Acceptors for Electron Donor–Acceptor Complex Photoactivation

“…The crucial step requires the effective turnover of the catalyst via SET oxidation of the catalyst radical anion, arising from the photoactivity of the progenitor EDA complex. A few recent reports used electron-poor catalysts to elicit EDA complex activation, but these catalysts only proved useful to activate specific radical precursors and were therefore limited to selected transformations.…”