Consecutive Multiphoton-Mediated Defluorinative Amination of Fluoroarenes

Traditional nucleophilic aromatic substitution (S_NAr) is a versatile tool for the construction of molecular complexity in (hetero)aromatic systems for fluoroarenes. However, it generally necessitates harsh reaction conditions to achieve the products. To overcome these drawbacks, we developed a robust and general method using a new strongly oxidizing photocatalyst, HATCN. The photocatalyst HATCN, built on a large π-delocalized aromatic core, can afford multiple stable redox states upon visible-light excitation and successive reductions under very mild potential. This modularity in affording multiple redox states proved instrumental in steering the aromatic defluorinative amination of fluorobenzenes. During the mechanistic study of this S_NAr reaction, it is apparent that altogether three photons are invested to conduct the full catalytic process, which is so far elusive in photochemically driven catalytic cycles. The two stable redox states of the photocatalyst are capable of oxidizing two substrate molecules that translates in the substrate versatility by accessing electron-neutral, electron-poor, and heterocyclic variants, which were previously inaccessible using established methods. Intriguingly, while the neutral and monoanionic HATCN acts as an oxidant, direduced HATCN behaves as a reductant. The critical evaluation of these redox states has been substantiated by intermediate redox-state isolation, along with a series of control reactions. Eventually, the cubic dependence of reaction rate on photon intensity demonstrated the consecutive three photon involvement in overall catalysis. The high efficiency of this oxidizing photocatalyst directly stems from its redox flexibility, which also translates to its unique mechanistic paradigm, involving multiphotons for the catalytic process.