Helical Carbenium Ion: A Versatile Organic Photoredox Catalyst in Red-Light-Mediated Reactions

Red light has the advantages of low energy, less health risk and high penetration depth through various media. Herein, a helical carbenium ion (N,N’-di-n-propyl-1,13-dimethoxyquinacridinium (ⁿPr-DMQA⁺) tetrafluoroborate) has been used as an organic photoredox catalyst for photoreductions and photooxidations in the presence of red light (λ_max = 640 nm). It has catalyzed red-light-mediated dual transition-metal/photoredox-catalyzed C-H arylation and intermolecular atom transfer radical addition through oxidative quenching, affording products in 57-93% yields. Moreover, its potential in photooxidation catalysis has also been demonstrated by successful applications in red-light-induced aerobic oxidative hydroxylation of arylboronic acids and benzylic C(sp³)-H oxygenation through reductive quenching, delivering products in up to 92% yield. Thus, a versatile organic photoredox catalyst (helical carbenium ion) for red-light-mediated photoredox reactions has been developed.