Spotlight on Photoinduced Aryl Migration Reactions

Abstract

Rearrangement reactions are certainly one of the most useful approaches towards complex structures in organic chemistry. With efficient conditions, it is indeed possible to convert simple substrates into highly functionalized products. Moreover, combining this approach with an attractive initiation process, such as visible‐light catalysis, makes these reactions particularly powerful. Recently, tremendous improvements have been made, owing to a better understanding of photoredox mechanisms. In this review, recent progress on visible‐light aryl migration reactions is discussed, focusing especially on Smiles rearrangement and related reactions.

Visible Light Mediated Photocatalytic N-Radical Cascade Reactivity of γ,δ-Unsaturated N-Arylsulfonylhydrazones: A General Approach to Structurally Diverse Tetrahydropyridazines

“…Furthermore, we tested the reactivity of mesitylhydrazones (mesityl = 2,4,6-trimethylphenyl) 12a – 12g and a completely different outcome was observed (Table ). Two products were recovered in high yields: the first ( 14a ) derived from the photocatalyzed cyclization of the N -hydrazonyl radical, and the second due to a photoradical promoted carboamination/Smiles rearrangement ( 15a ). − Best results were obtained with 2,2-dimethylbut-3-enylphenylmesitylhydrazone ( 12a ) and 2,2-dimethylbut-3-enylmethylmesitylhydrazone ( 12e ) with a total yield of 95% and a ratio of 53:47 and 61:39 between products 14a / 15a and 14e / 15e , respectively, again demonstrating no difference between aromatic and aliphatic derivatives (Table ). When 2-naphthyl ( 12b ) was introduced as the substituent, 72% yield was obtained and a ratio of 58:42 between the cyclization product 14b and the Smiles rearrangement 15b .…”

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.…”

“…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.…”

“…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.…”