Electrochemical Reductive Smiles Rearrangement for C–N Bond Formation

Electrosynthesis of 1,2,3-Benzotriazines through an Iodide-Catalyzed Skeletal Editing of 3-Aminoindazoles

This report describes an environmentally benign synthesis of 1,2,3-benzotriazines through an iodide-catalyzed electro-oxidative N-centered [1,2]-rearrangement of 3-aminoindazoles. The developed method demonstrates the activation of heteroatoms via electrochemically generated reactive iodide species without using any metal catalysts and peroxides. The protocol features practical and mild reaction conditions and displays a wide substrate scope. Various mechanistic experiments and cyclic voltammetric studies have been instrumental in elucidating the reaction mechanism, operating via a skeletal rearrangement of 3-aminoindazoles.

The merger of electro-reduction and hydrogen bonding activation for a radical Smiles rearrangement

The reductive activation of chemical bonds at less negative potentials provides a foundation for high functional group tolerance and selectivity, and it is one of the central topics in organic electrosynthesis. Along this line, we report the design of a dual-activation mode by merging electro-reduction with hydrogen bonding activation. As a proof of principle, the reduction potential of N-phenylpropiolamide was shifted positively by 218 mV. Enabled by this strategy, the radical Smiles rearrangement of N-arylpropiolamides without external radical precursors and prefunctionalization steps was accomplished. [DBU][HOAc], a readily accessible ionic liquid, was exploited for the first time both as a hydrogen bonding donor and as a supporting electrolyte.

Recent advances in the electrochemical reactions of nitrogen-containing organic compounds

The electrochemical reaction of amines, nitriles, amides, nitroaromatics, and imines has been proven to be a valuable method for the synthesis of various nitrogen-containing organic compounds.

Transition Metal-Free, Methoxide-Catalyzed Synthesis of Pyridoindolones

A simple transition metal-free strategy for the synthesis of pyrido[1,2-a]indolone derivatives has been devised through sodium methoxide-catalyzed intramolecular cyclization of 2-alkenylated N-pyrimidyl indoles. The reactions involved a Smiles rearrangement/cyclization cascade, which resulted in a new series of N-fused indoles, potentially applicable skeletons in medicinal chemistry. This reaction presents simple eco-friendly reaction conditions, a high atom- and cost-economy, a short reaction time, and a broad range of substrate scope with high reaction efficiency.

Electrodimerization of N-Alkoxyamides for the Synthesis of Hydrazines

An efficient and valuable N-N dimerization reaction of N-alkoxyamides is reported under undivided electrolytic conditions. This electrochemical strategy provides a powerful way to access a wide range of advanced, highly functionalized hydrazines. Remarkably, an N-centered radical generated from the cleavage of the N-H bond under electrolytic conditions plays a crucial role in this transformation. Furthermore, various N-alkoxyamides bearing different substituents are suitable in this transformation, furnishing the corresponding hydrazines in up to 92% yield.

Photocatalytic intermolecular carboarylation of alkenes by selective C-O bond cleavage of diarylethers

Disclosed herein is a novel radical-mediated intermolecular carboarylation of alkenes by cleaving inert C-O bonds. The strategically designed arylbenzothiazolylether diazonium salts are harnessed as dual-function reagents. A vast array of alkenes are proven to be suitable substrates. The benzothiazolyl moiety in the products serves as the formyl precursor, and the OH residue provides the cross-coupling site for further product elaboration, indicating the robust transformability of the products.

Copper-Catalyzed Aminoheteroarylation of Unactivated Alkenes through Distal Heteroaryl Migration

We report a copper-catalyzed aminoheteroarylation of unactivated alkenes to access valuable heteroarylethylamine motif. The developed reaction features a copper-catalyzed intermolecular electrophilic amination of the alkenes followed by a migratory heteroarylation. The method applies on alcohol-, amide-, and ether-containing alkenes, overcoming the common requirement of a hydroxyl motif in previous migratory difunctionalization reactions. This reaction is effective for the introduction of diverse aliphatic amines and has good functional group tolerance, which is particularly useful for richly functionalized heteroarenes. This migration-involved reaction was found well suited as a powerful ring expansion approach for the construction of medium-sized rings that are in great demand in medicinal chemistry.

Visible-Light-Driven Aryl Migration and Cyclization of α-Azido Amides

This paper reports two new visible-light-promoted radical reactions of α-azido amides. By catalysis of [Ir(ppy)₂(dtbbpy)]PF₆ with i-Pr₂NEt as the reducing agent, N-aryl α-azido tertiary amides were first converted to the corresponding aminyl radicals through reduction of the azido group; the aminyl radicals then underwent N-to-N aryl migration to give α-anilinyl-functionalized amides. α-Azido secondary amides, on the other hand, reacted with the solvent ethanol and i-Pr₂NEt to afford the imidazolinone products.

Electro-Oxidative Coupling Reactions Leading to π-Conjugated Compounds

Electrochemical reactions are rapidly gaining attention today as a powerful and environmentally benign reaction processes for organic synthesis. We found that the electro-oxidation of palladium acetate afforded cationic palladium species and thus-generated cationic Pd species were efficient mediators for electro-oxidative coupling reactions. Homo-coupling of arylboronic acids and terminal alkynes proceeded efficiently to afford biaryls and butadiyne, respectively. Cross-coupling reactions between terminal alkynes and arylboronic acids were also achieved with the use of a Ag anode. As an advantage of electrochemical reactions, we developed a sequential reaction system switched between oxidative and neutral conditions by the on/off application of electricity, and several π-extended butadiynes were obtained in one-sequence by the system. Electrochemical intramolecular C-S coupling for the synthesis of thienoacene was also developed. The use of Bu₄ NBr as a halogen mediator was essential for the reaction.

Electrochemical rearrangement protocols towards the construction of diverse molecular frameworks

Rearrangement reactions constitute a critical facet of synthetic organic chemistry and demonstrate an attractive way to take advantage of existing structures to access various important molecular frameworks. Electroorganic chemistry has emerged as an environmentally benign approach to carry out organic transformations by directly employing an electric current and avoids the use of stoichiometric chemical oxidants. The last few years have witnessed a resurgence of electroorganic chemistry that has promoted a renaissance of interest in the development of novel redox electroorganic transformations. This review manifests the evolution of electrosynthesis in the area of rearrangement chemistry and covers the achievements in the field of migration, ring expansion, and rearrangements along with the mechanisms involved.

Electrochemical access to benzimidazolone and quinazolinone derivatives via in situ generation of isocyanates

Isocyanates are the key intermediates for several organic transformations towards the synthesis of diverse pharmaceutical targets. Herein, we report the development of an oxidant-free protocol for electrochemical in situ generation of isocyanates. This strategy highlights expedient access to benzimidazolones and quinazolinones and eliminates the need for exogenous oxidants. Furthermore, detailed mechanistic studies provide strong support towards our hypothesis of in situ isocyanate generation.

C- to N-Center Remote Heteroaryl Migration via Electrochemical Initiation of N Radical by Organic Catalyst

Herein an exogenous oxidant- and metal-free electrochemical heteroaryl migration triggered by N radicals to construct new N-C bonds was developed. This methodology features a high atom economy and utilization rate of energy, and it is insensitive to water and air. Moreover, a user-friendly undivided cell was employed. The use of an organic catalyst makes it more efficient, green, and practical.

Visible light-mediated Smiles rearrangements and annulations of non-activated aromatics

Novel and efficient visible light-mediated Smiles rearrangements and annulations progressing via a radical-cation intermediate catalytically generated with an acridinium salt.

A metal- and oxidizing-reagent-free anodic para-selective amination of anilines with phenothiazines

A highly para-selective amination of anilines with phenothiazines for producing various functionalized 10-aryl-10H-phenothiazines is reported.