# Photothermal Conversion Promotes Challenging SNAr for Facile C─N Bond Formation

## TL;DR

This paper introduces a new method using light and heat to efficiently form C─N bonds in challenging chemical reactions.

## Contribution

The study introduces photothermal conversion with red light and carbon black to enable efficient SNAr reactions for C─N bond formation.

## Key findings

- Photothermal conversion with red light and carbon black enables SNAr reactions with poorly activated electrophiles.
- Intramolecular SNAr reactions occurred rapidly, suggesting localized heating effects.
- A sequential SNAr approach was developed to form fused heterocycles efficiently.

## Abstract

Nucleophilic aromatic substitution (SNAr) 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 SNAr 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 SNAr, 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.

Photothermal conversion enables facile aromatic C─N bond formation via red light irradiation. A variety of inter‐ and intramolecular SNAr transformations are achieved under mild, schematically simple conditions. Additionally, a thermally promoted halogen exchange mechanism provides access to aryl bromides, chlorides, and fluorides – making this approach an excellent synthetic tool for forming aromatic C─N bonds.