Cobalt-Catalyzed 1,4-Aryl Migration/Desulfonylation Cascade: Synthesis of α-Aryl Amides

Photocatalytic Asymmetric Acyl Radical Truce-Smiles Rearrangement for the Synthesis of Enantioenriched α-Aryl Amides

The radical Truce-Smiles rearrangement is a straightforward strategy for incorporating aryl groups into organic molecules for which asymmetric processes remains rare. By employing a readily available and non-expensive chiral auxiliary, we developed a highly efficient asymmetric photocatalytic acyl and alkyl radical Truce-Smiles rearrangement of α-substituted acrylamides using tetrabutylammonium decatungstate (TBADT) as a hydrogen atom-transfer photocatalyst, along with aldehydes or C-H containing precursors. The rearranged products exhibited excellent diastereoselectivities (7 : 1 to >98 : 2 d.r.) and chiral auxiliary was easily removed. Mechanistic studies allowed understanding the transformation in which density functional theory (DFT) calculations provided insights into the stereochemistry-determining step.

Radical-Mediated α-tert-Alkylation of Aldehydes by Consecutive 1,4- and 1,3-(Benzo)thiazolyl Migrations

The direct alkylation of the α-position of aldehydes is an effective method for accessing a wide range of structurally diverse aldehydes, yet tert-alkylation has proven to be a challenging task. In this study, we present a novel radical-mediated tert-alkylation approach targeting the α-position of aldehydes, enabling the synthesis of complex aliphatic aldehydes. The transformation is initiated by the interaction between an in situ generated enamine intermediate and α-bromo sulfone, forming an electron donor-acceptor (EDA) complex, followed by consecutive 1,4- and 1,3-functional group migrations. This protocol operates under metal-free and mild photochemical conditions, delivering a broad scope of products and providing new mechanistic insights into radical rearrangement reactions.

An NHC-Catalyzed Desulfonylative Smiles Rearrangement of Pyrrole and Indole Carboxaldehydes

The use of catalysis methods to enable Smiles rearrangement opens up new substrate classes for arylation under mild conditions. Here, we describe an N-heterocyclic carbene (NHC) catalysis system that accesses indole and pyrrole aldehyde substrates in a desulfonylative Smiles process. The reaction proceeds under mild, transition-metal-free conditions and captures acyl anion reactivity for the synthesis of a diverse array of 2-aroyl indoles and pyrroles from readily available sulfonamide starting materials.

Heteroarylation of Congested α-Bromoamides with Imidazo-Heteroarenes and Indolizines via Aza-Oxyallyl Cations: Enroute to Dibenzoazepinone and Zolpidem Analogues

Herein, we report a highly efficient and unprecedented approach for heteroarylation of congested α-bromoamides via electrophilic aromatic substitution of imidazo-heteroarenes and indolizines under mild reaction conditions (room temperature, metal, and oxidant free). The participation of an in situ generated aza-oxyallyl cation as an alkylating agent is the hallmark of this transformation. The method was readily adapted to synthesize novel imidazo-heteroarene-fused dibenzoazepinone architectures of potential medicinal value.

Synthese von α-Arylacrylamiden via Lewis Base vermitteltem Aryl/Wasserstoff-Austausch

Hierin stellen wir eine neue Methode für die Synthese von α‐Arylacrylamiden vor. Die Reaktion basiert auf der Nutzung polarer S‐zu‐C Arylwanderungen, induziert durch einen Lewis‐basischen Organokatalysator. Im Unterschied zu zuvor publizierten radikalischen Arylwanderungen von Sulfonylacrylamiden, ermöglicht dieser polare Prozess eine darauffolgende Eliminierung, wodurch in Summe ein formaler Aryl/Wasserstoff‐Austausch unter Ausscheidung von SO2 stattfindet. Die vorgestellte Reaktion ist selektiv für elektronenarme aromatische Gruppen, während eine Vielfalt von Substituenten am Stickstoff und an der β‐Position toleriert werden, und erzeugt nützliche Bausteine für Folgereaktionen wie Zykloadditionen und Zyklisierungen. Der Reaktionsmechanismus wurde mithilfe quantenchemischer Berechnungen erforscht, die die unerwartete Rolle der Lewis Base in mehreren Schlüsselschritten darlegten.

Synthesis of α-Aryl Acrylamides via Lewis-Base-Mediated Aryl/Hydrogen Exchange

Herein we report a method for the synthesis of α-aryl acrylamides leveraging polar S-to-C aryl migrations induced by a Lewis basic organocatalyst. In contrast to previously reported radical aryl migrations of sulfonyl acrylimides, this polar process enables subsequent elimination, ultimately leading to a formal aryl/hydrogen exchange including SO2 extrusion. This reaction is selective for electron-deficient aromatic groups, while tolerating a variety of substituents on nitrogen and in the β-position, and it delivers useful building blocks for further transformations, including cycloaddition and cyclisation reactions. The mechanism was investigated in detail using quantum chemical calculations, which unexpectedly revealed the Lewis base to be involved in several decisive steps.

SO2-Extrusive 1,4-(Het)Aryl Migration: Synthesis of α-Aryl Amides and Related Reactions

(Het)aryl migration has emerged as a key synthetic tool and has particularly been exploited for the synthesis of α-aryl amides. This method overcomes the existing α-arylation methods, which are not always compatible with the introduction of (het)aryl groups possessing bulky or electrophilic substituents. This review focuses on SO2-extrusive (het)aryl migration in the frame of α-aryl amide synthesis. Anion- and radical-mediated transformations are reported, including the synthesis of polycyclic compounds through cascade reactions.

1 Introduction

2 Anionic Aryl Migration

3 Radical Aryl Migration

4 Conclusion

Recent Advances in the Smiles Rearrangement: New Opportunities for Arylation

The Smiles rearrangement has undergone a renaissance in recent years providing new avenues for non-canonical arylation techniques in both the radical and polar regimes. This short review will discuss recent applications of the reaction (from 2017 to late 2021), including its relevance to areas such as heterocycle synthesis and the functionalization of alkenes and alkynes as well as glimpses at new directions for the field.

1 Introduction

2 Polar Smiles Rearrangements

3 Radical Smiles: Alkene and Alkyne Functionalization

4 Radical Smiles: Rearrangements via C–X Bond Cleavage

5 Radical Smiles: Miscellaneous Rearrangements

6 Conclusions

Diarylamine Synthesis via Desulfinylative Smiles Rearrangement

Diarylamines are obtained directly from sulfinamides through a novel rearrangement sequence. The transformation is transition metal-free and proceeds under mild conditions, providing facile access to highly sterically hindered diarylamines that are otherwise inaccessible by traditional S_NAr chemistry. The reaction highlights the distinct reactivity of the sulfinamide group in Smiles rearrangements versus that of the more common sulfonamides.