Triaryl-Heptazine Photocatalysts for the Oxidation of C–H and C–C Bonds in Nitrogen-Containing Molecules

Open-shell intermediates have become central to modern organic synthesis, placing photoredox catalysis, and therefore the development of photocatalysts, as a crucial area of research. We report the development of a photocatalytic platform based on triaryl-heptazines, which possess a high level of tunability and high potency for oxidation reactions. A representative set of four photocatalysts from this family were synthesized and fully characterized (UV–vis absorption and emission spectroscopy, cyclic voltammetry, and time-correlated single-photon counting) showing high excited-state reduction potentials and long excited-state lifetimes. DFT and time-dependent DFT studies were performed and account for the observed photochemical properties. One of these photocatalysts was then used for oxidative transformations of nitrogen-containing molecules, namely, N-methyl oxidation to N-formyl compounds and C–C bond cleavage of cyclic N-protected amines. In both cases, this triaryl-heptazine catalyst displays synthetically significant features, notably in terms of selectivity and substrate scope. Moreover, mechanistic investigations provided valuable insights into the behavior of this photocatalyst in the reaction.