An Investigation of the Photoredox Radical Smiles Rearrangement

Abstract

Photoredox catalysis is the core interest in our study of radical Smiles rearrangements across this work. The radical Smiles rearrangement is a robust reaction used for sp3-sp2 and sp2-sp2 coupling and we aimed to use visible light energy to operate this transformation, using cheap and abundant carboxylic acid derivatives as starting materials. Multiple ways of radical generation were used when investigating the radical Smiles rearrangement on sulfonates and sulfonamides. In the visible-light mediated intramolecular aryl-aryl coupling of aryl sulfonamidobenzoic acids (a), pyridine was identified to be an effective base in deprotonating the benzoic acid in one of the aryl sulfonylamidobenzoic acid substrates. This facilitated the decarboxylation of the in-situ generated benzoate-hypobromite intermediate, leading to aryl radical generation. Rather than the aryl-aryl Smiles coupling, the generated aryl radical preferred two other quenching pathways: either hydrogen abstraction or pyridine coupling. Distant cyano-alkyl radical generation from cyclobutyloxime cleavage (b) was used in the investigation of the intramolecular tandem Smiles rearrangement while alkyl decarboxylative generation of radicals from alkyl N-hydroxyphthalimide (c) was used in the study of the intermolecular approach on a sulfonyl methacrylamide. Surprisingly, the alkene functional group in both cases was found to be unstable in our mild photo conditions. The maleimide-like alkene was found to be sensitive to trialkylamine base while the alkene in the methacrylamide was found to interrupt the designed alkyl decarboxylative photocatalytic system.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	David Procter (Supervisor) & Michael Greaney (Supervisor)