Metal-free 2-isocyanobiaryl-based cyclization reactions: phenanthridine framework synthesis

The development of transition metal-free 2-isocyanobiaryl-based reactions has received much attention due to the widespread presence of phenanthidine frameworks as products in pharmacological chemistry and materials science. This review article focuses on the achievements from 2013 until now in various metal-free catalyzed reactions and discusses challenging mechanisms and features of the transformations.

Electrochemical Post-Ugi Cyclization for the Synthesis of Highly Functionalized Spirolactams

The combination of the Ugi reaction and electro-organic synthesis can aid in the creation of novel heterocycles that have not been previously explored. In this study, a new strategy utilizing bis-amides from the Ugi reaction has been developed, which can produce C-S, C-Se, and C-C═O functionalized five-membered spirolactams mediated by electricity under catalyst- and metal-free conditions. Notably, this approach can be applied using a microelectro-flow reactor (μ-EFR) for gram-scale synthesis. The described strategy can synthesize complex azaspiro-fused tricyclic scaffolds with high diastereo- and regioselectivity, highlighting its versatility and potential.

Crafting mono- and novel bis-methylated pyrroloquinoxaline derivatives from a shared precursor and its application in the total synthesis of marinoquinoline A

The synthesis of mono- and novel bis-methylated pyrrolo[1,2-a]quinoxalines through the addition of unstable methyl radicals to aryl isocyanides is described contingent upon the reaction conditions employed. The strategy has been effectively employed in the total synthesis of the natural product marinoquinoline A.

Recent advances in electrochemical functionalization using diazonium salts

Arenediazonium salts have gained attention in the scientific community due to their numerous synthetic applications. In the traditional method of dediazoniation of arenediazonium salts, the requirements for toxic oxidants and costly catalysts affect their cost-effectiveness and sustainability. However, recent advances in synthetic organic electrochemistry allow for the in situ reduction of arenediazonium salts, affording different functionalizations under mild reaction conditions and with a shorter reaction time. Herein, we report advances up to now of facile organic electrochemical syntheses using arenediazonium salt precursors that avoid the use of hazardous reductants.

Visible-Light-Induced Annulation of Iodonium Ylides and 2-Isocyanobiaryls to Access 6-Arylated Phenanthridines

A 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4-CzIPN)-photocatalyzed cascade arylation/cyclization reaction of 2-isocyanobiaryls and iodonium ylides was established for the synthesis of 6-arylated phenanthridines. This is the first example of employing iodonium ylides as aryl radical sources in a visible-light-induced radical cascade cyclization reaction.

Mn-catalyzed electrooxidative radical phosphorylation of 2-isocyanobiaryls

As an efficient and green synthesis method, the electrocatalysis hydrogen evolution coupling reaction has been widely used by chemists to realize the combining of two nucleophiles. In this work, an alternative method to synthesize 6-phosphorylated phenanthridines has been developed by synergistically utilizing electrocatalysis and Mn catalysis, with moderate to relatively good yields achieved. Mild and oxidant-free conditions make this synthetic method applicable in various settings.

Recent Advances in the Electrochemical Functionalization of Isocyanides

Isocyanides are well-known as efficient CO surrogates and C1 synthons in modern organic synthesis. Although tremendous efforts have been devoted to fully exploiting the reactivity of isocyanides, these transformations are primarily limited by their utilization of stoichiometric toxic chemical oxidants. With the recent resurgence of organic electrochemistry, which has considerably laid dormant over the past several decades, electrolysis has been identified as a green and powerful tool to enrich structural diversity by solely utilizing electric current as clean and inherently safe redox equivalents of stoichiometric chemical oxidants. In this regard, the unique reactivity of isocyanides has been studied in numerous electrochemical transformations. This review comprehensively highlights the most relevant progress in electrochemical strategies towards the functionalization of isocyanides up until June of 2022, with a focus on reaction outcomes and mechanisms.

Electrochemical Regioselective Sulfenylation of 2H-Indazoles with Thiols in Batch and Continuous Flow

A novel electrochemical cross-dehydrogenative C-S bond coupling of aryl thiols with 2H-indazole is reported. Thiol-functionalized 2H-indazoles were synthesized under catalyst-, oxidant-, and metal-free conditions with innocuous hydrogen as the sole byproduct at ambient temperature. Furthermore, continuous electrochemical flow conditions using a graphite/Ni flow cell were used to obtained 3-(arylthio)-2H-indazole compounds on a gram scale within the residence time of 39 min. Detailed mechanistic studies including control experiments and cyclic voltammetry are provided to support the radical-radical cross-coupling pathway.

Electrochemical synthesis for α-arylation of ketones using enol acetates and aryl diazonium salts

In this article, an electrochemical method has been developed to achieve the α-arylation of ketones by reacting aryl diazonium salts with enol acetates. The broad scope of the reaction toward...