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Photothermal conversion enables thermal gradients that facilitate high activation barrier reactions, such as the Newman Kwart Rearrangement. Substrates normally requiring bulk temperatures >250 °C are easily converted via visible light irradiation with short reaction times. Wavelength and intensity tunability enable selective product formation.

Photothermal Conversion by Carbon Black Facilitates Aryl Migration by Photon‐Promoted Temperature Gradients

Megan E Matter, Lejla Čamdžić, and Erin E. Stache

Angew. Chem. Int. Ed. 2023, e202308648

Communication

Publication Abstract

The Newman Kwart Rearrangement (NKR) offers an efficient and high-yielding method for producing substituted thiophenols from phenols. While an industrially important protocol, it suffers from high activation energy barriers (35-43 kcal/mol), requiring the use of extreme temperatures (>200 °C) and specialty equipment. This report details a highly efficient and straightforward method for facilitating the NKR using photothermal conversion. This underused, unique reactivity pathway arises from the irradiation of nanomaterials that relax via a non-radiative decay pathway to generate intense thermal gradients. We show carbon black (CB) can be an inexpensive and abundant photothermal agent under visible light irradiation to achieve a facile NKR under mild conditions. The scope includes a wide array of stereo- and electronically diverse substrates with increasing difficulty of rearrangement, including BHT and BINOL as effective substrates. Furthermore, we demonstrate the unique application for temporal control in a thermal reaction and tunability of thermal gradients by modulating light intensity. Ultimately, photothermal conversion enables high-temperature reactions with simple, visible light irradiation.