Photothermal Conversion Promotes Challenging S_NAr for Facile C─N Bond Formation

Nucleophilic aromatic substitution (S_NAr) is a widely used method for forming aromatic C─N bonds, which are of interest in both industry and academia. However, current approaches are often unable to access less activated electrophiles, due to negative charge buildup in the transition state, resulting in high activation energy barriers. Inspired by our work on the Newman Kwart Rearrangement (NKR), we sought to leverage photothermal conversion for challenging C─N bond-forming S_NAr reactions. Here, we demonstrate that the incorporation of an inexpensive photothermal agent, carbon black, and irradiation with red light affords several poorly activated intermolecular substitution reactions. Application to less activated aryl halides resulted in unproductive reactivity, leading us to examine the reaction barriers. Computations revealed barriers within the range previously achieved during our photothermally mediated NKR. Electronically neutral intramolecular analogs were synthesized and underwent productive reactivity in short time frames (≤20 min), indicating that the inhomogeneous nature of photothermal heating was a challenge in terms of colocalizing reactants sufficiently close to the particle. This concept was leveraged into a sequential S_NAr, where an initial intermolecular reaction occurs which then primes the substrate for a more difficult intramolecular substitution. This approach afforded a diverse scope of fused heterocycles.