Visible‐Light‐Induced C2 Alkylation of Heterocyclic N‐Oxides with N‐Hydroxyphthalimide Esters under Metal‐Free Conditions

Visible-light-mediated synthesis of oxime esters via multicomponent reactions of aldehydes, aryl amines, and N-hydroxyphthalimide esters

Oxime esters are useful scaffolds in many organic chemistry transformations. Herein, a novel visible-light-mediated three-component reaction for synthesis of oxime esters is reported. Aldehydes, aniline, and N-hydroxyphthalimide (NHPI) esters were used as substrates in this three-component reaction, and eosin Y was used as a crucial photocatalyst for the reaction. Wide ranges of aldehydes and NHPI esters were well tolerated in this reaction method, generating various oxime esters with high efficiency under mild reaction conditions. This visible-light-mediated methodology will be a promising approach to synthesize useful oxime esters in a single step.

Recent Advances in Catalytic and Technology-Driven Radical Addition to N,N-Disubstituted Iminium Species

Recently, radical chemistry has grown exponentially in the toolbox of organic synthetic chemists. Upon the (re)introduction of modern catalytic and technology-driven strategies, the implementation of highly reactive radical species is currently facilitated while expanding the scope of numerous synthetic methodologies. In this context, this review intends to cover the recent advances in radical-based transformations of N,N-disubstituted iminium substrates that encompass unique reactivities with respect to imines or protonated iminium salts. In particular, we have focused on the literature concerning the dipole type substrates, such as nitrones or azomethine imines, together with the chemistry of N⁺-X^- (X = O, NR) azaarenium dipoles, which proved to be very versatile platforms in that field of research. The N-alkylazaarenium salts were been considered, which demonstrated specific reactivity profiles in radical chemistry.

Exploiting photoredox catalysis for carbohydrate modification through C–H and C–C bond activation

Photoredox catalysis has recently emerged as a powerful synthetic platform for accessing complex chemical structures through non-traditional bond disconnection strategies that proceed through free-radical intermediates. Such synthetic strategies have been used for a range of organic transformations; however, in carbohydrate chemistry they have primarily been applied to the generation of oxocarbenium ion intermediates in the ubiquitous glycosylation reaction. In this Review, we present more intricate light-induced synthetic strategies to modify native carbohydrates through homolytic C-H and C-C bond cleavage. These strategies allow access to glycans and glycoconjugates with profoundly altered carbohydrate skeletons, which are challenging to obtain through conventional synthetic means. Carbohydrate derivatives with such structural motifs represent a broad class of natural products integral to numerous biochemical processes and can be found in active pharmaceutical substances. Here we present progress made in C-H and C-C bond activation of carbohydrates through photoredox catalysis, focusing on the operational mechanisms and the scope of the described methodologies.

General electrochemical Minisci alkylation of N-heteroarenes with alkyl halides

Herein, we report, a general, facile and environmentally friendly Minisci-type alkylation of N-heteroarenes under simple and straightforward electrochemical conditions using widely available alkyl halides as radical precursors. Primary, secondary and tertiary alkyl radicals have been shown to be efficiently generated and coupled with a large variety of N-heteroarenes. The method presents a very high functional group tolerance, including various heterocyclic-based natural products, which highlights the robustness of the methodology. This applicability has been further proved in the synthesis of various interesting biologically valuable building blocks. In addition, we have proposed a mechanism based on different proofs and pieces of electrochemical evidence.

Electron donor–acceptor complex-catalyzed photoredox reactions mediated by DIPEA and inorganic carbonates

A DIPEA–NHPI ester–inorganic carbonate catalytic EDA complex is reported as an efficient and sustainable radical generation platform for developing photocatalytic reactions.

Photoredox-Catalysed Regioselective Synthesis of C-4-Alkylated Pyridines with N -(Acyloxy)phthalimides

A method of direct C-4 selective alkylation of pyridine under visible light irradiation at room temperature was reported, using simple maleate-derived pyridinium salts as pyridine precursors, and the readily available...

Photoredox Generation of N-Centered Hydrazonyl Radicals Enables the Construction of Dihydropyrazole-Fused gem-Difluoroalkenes

An efficient visible-light-promoted N-radical-mediated tandem radical cyclization/defluorinated alkylation of β,γ-unsaturated hydrazones, and α-trifluoromethyl alkenes is described. This protocol provides a general and effective route to synthesize various dihydropyrazole-fused gem-difluoroalkenes at moderate to excellent yields under redox-neutral, metal-free, and mild conditions.

An ultrastable olefin-linked covalent organic framework for photocatalytic decarboxylative alkylations under highly acidic conditions

An ultrastable olefin-linked covalent organic framework 2D-COF-2 offers an alternative heterogeneous photocatalyst for photocatalytic decarboxylative alkylations, exhibiting impressive effciency, sustainabilty and promising industrial potential.