Aryl Transfer Strategies Mediated by Photoinduced Electron Transfer

Abstract

Radical aryl migrations are powerful techniques to forge new bonds in aromatic compounds. The growing popularity of photoredox catalysis has led to an influx of novel strategies to initiate and control aryl migration starting from widely available radical precursors. This review encapsulates progress in radical aryl migration enabled by photochemical methodsparticularly photoredox catalysissince 2015. Special attention is paid to descriptions of scope, mechanism, and synthetic applications of each method.

Recent Advances in the Smiles Rearrangement: New Opportunities for Arylation

“…In the radical manifold, the ability for electrophilic, open-shell species to undergo intra-and intermolecular bond formation with unsaturated systems can enable expedient access to radical Smiles intermediates. [4][5][6] The resulting products allow for sp 3 -sp 3 and sp 2 -sp 3 bonds to be forged in a single step. Exploiting photoredox catalysis for the generation of the initial single-electron species allows for exceptional operational mildness in comparison to alternative strategies for sp 3 -aryl formation.…”

“…Previous reviews on the topic [1][2][3][4][5][6] have detailed the key advances in the field, such as the rearrangement's applicability to biaryl syntheses, [18][19][20] the use of the rearrangement in heterocyclic syntheses and also the use of the reaction as a tandem bond-forming process. [21][22][23] This Short Review will aim to recount the key advances that have been made since 2017.…”

“…Previous reviews on the topic [1][2][3][4][5][6] have detailed the key advances in the field, such as the rearrangement's applicability to biaryl syntheses, [18][19][20] the use of the rearrangement in heterocyclic syntheses, and also the use of the reaction as David Whalley, originally from Northamptonshire, England began his studies in Chemistry at the University of Nottingham with a year abroad at the National University of Singapore. He undertook his Masters project studying natural product synthesis with Professor Christopher Moody.…”

“…The Smiles rearrangement is an intramolecular nucleophilic aromatic ipso-substitution reaction, enabling aryl migration to take place. [1][2][3][4][5][6] The original incarnation of the reaction used anionic heteroatomic species as the incoming nucleophile (Scheme 1, conversion of 1 to 2), until Dohmori and Truce demonstrated the reaction's applicability to carbon-centered nucleophiles (Scheme 1, 3 to 4 and 5 to 6, respectively). [7][8][9][10][11] This key advancement led to Smiles chemistry being utilized for C-C bond formation in decades to come, with pivotal contributions from Speckamp and Motherwell demonstrating that the reaction can also operate via a radical pathway.…”

Catalytic intramolecular aminoarylation of unactivated alkenes with aryl sulfonamides

“…Aryl migrations have become increasingly accessible to synthetic chemists as modern photochemical techniques have matured. [26][27][28] In this case, the migration would grant entry to the arylethylamine scaffold from inexpensive sulfonamides. 29,30 Mechanistically, this distinct cascade would not require a crosscoupling catalyst and may grant access to sterically congested products that are challenging to prepare through transition metal-mediated methods.…”