Anodic Oxidation of Aminotetrazoles: A Mild and Safe Route to Isocyanides

Atroposelective synthesis of axially chiral imidazo[1,2-a]pyridines via asymmetric multicomponent reaction

Imidazo[1,2-a]pyridines are privileged heterocycles with diverse applications in medicinal chemistry; however, the catalytic asymmetric synthesis of these heterocyclic structures remains underexplored. Herein, we present an efficient and modular approach for the atroposelective synthesis of axially chiral imidazo[1,2-a]pyridines via an asymmetric multicomponent reaction. By utilizing a chiral phosphoric acid catalyst, the Groebke-Blackburn-Bienaymé reaction involving various 6-aryl-2-aminopyridines, aldehydes, and isocyanides gave access to a wide range of imidazo[1,2-a]pyridine atropoisomers with high to excellent yields and enantioselectivities. Extensive control experiments underscored the pivotal role of the remote hydrogen bonding donor on the substrates in achieving high stereoselectivity for these reactions. The versatile derivatizations of these atropisomeric products, especially their role as an analog of NOBINs and their facile conversion into unique 6,6-spirocyclic products, further emphasize the merits of this methodology.

eCyanation Using 5-Aminotetrazole As a Safer Electrophilic and Nucleophilic Cyanide Source

An electrochemical method for carrying out safer cyanation reactions is reported. The use of 5-aminotetrazole as a cyanide source enabled the successful electrogeneration of both electrophilic and nucleophilic cyanide sources. To demonstrate the versatility of the method, a variety of cyanation reactions were carried out, including the synthesis of cyanamides, N-heterocycles, and aromatic nitriles, as well as the nucleophilic addition of cyanides to a variety of electrophiles without the need to handle highly toxic cyanide salts. Finally, as a proof of concept for scalability, the cyanation methodology was rapidly transferred to a flow electrosynthesis setup, which demonstrated its potential for large-scale applications.

Unified Approach to Deamination and Deoxygenation Through Isonitrile Hydrodecyanation: A Combined Experimental and Computational Investigation

Herein, we describe a general hydrodefunctionalization protocol of alcohols and amines through a common isonitrile intermediate. To cleave the relatively inert C-NC bond, we leveraged dual hydrogen atom transfer (HAT) and photoredox catalysis to generate a nucleophilic boryl radical, which readily forms an imidoyl radical intermediate from the isonitrile. Rapid β-scission then accomplishes defunctionalization. This method has been applied to the hydrodefunctionalization of both amine and alcohol-containing pharmaceuticals, natural products, and biomolecules. We extended this approach to the reduction of carbonyls and olefins to their saturated counterparts, as well as the hydrodecyanation of alkyl nitriles. Both experimental and computational studies demonstrate a facile β-scission of the imidoyl radical, and reconcile differences in reactivity between nitriles and isonitriles within our protocol.

Exploiting the Different Nucleophilicity of the Isocyano Group: A Strategy for the Isocyanide Functionalization

By exploiting the different nucleophilicity of aromatic and aliphatic isocyanides, we selectively react aliphatic isocyano groups while preserving aromatic ones in Passerini and Ugi multicomponent reactions. This simple approach allows the synthesis of α-acyloxy carboxamides or α-acylamino carboxamides possessing one or two isocyanide groups, which are challenging to achieve through traditional formylation and dehydration protocols. These analogues have the potential to serve as valuable building blocks with diverse applications.

Palladium-Catalyzed Reductive Formylation of Aryl Iodides with CO2 under Mild Conditions

A palladium-catalyzed reductive formylation of aryl iodides with carbon dioxide as the carbonyl source under mild reaction conditions was realized by using a combination of Pd(PCy₃)₂Cl₂ and di-2-pyridyl ketone as the catalyst and phenylsilane as the reductive reagent, leading to a variety of aromatic aldehydes in moderate to excellent yields. The protocol features wide substrate scope, good functional group tolerance, and simple operation.

Electrochemical Benzylic C-H Functionalization with Isocyanides

We report the challenging direct carbamoylation or cyanation of benzylic C(sp³)-H bonds with an isocyanide via an electrochemical process giving rise to structures that are encountered in several biologically relevant compounds and drugs. This transformation proceeds under mild conditions without the need for any external oxidant and avoids the necessity to start from a prefunctionalized benzylic substrate or the deployment of the cation pool method. The anodic oxidation of the benzylic position and the subsequent addition of the isocyanide lead to the formation of a C-C bond and to a nitrilium cation that hydrolyzes to yield α-aryl acetamide derivatives, whereas the elimination of a t-butyl cation delivers α-aryl acetonitrile derivatives.