Preparation of α-Acyloxy Ketones via Visible-Light-Driven Aerobic Oxo-Acyloxylation of Olefins with Carboxylic Acids

Annulative coupling of α-substituted acrylic acids and sulfoxonium ylides: easy access to bioactive γ-butyrolactones

We present a straightforward, catalyst- and additive-free method for synthesizing keto γ-butyrolactones using readily available β-keto sulfoxonium ylides and acrylic acids. This robust approach demonstrates exceptional compatibility with various functional groups on β-keto sulfoxonium ylides and α-substituted acrylic acids, resulting in good to high yields of the anticipated products. Moreover, the practicality of this approach was validated through large-scale reactions and the successful conversion of some synthesized derivatives into bioactive natural products, including L-factor, muricatacin, and cytosporanone A.

Influence of N-protonation on electronic properties of acridine derivatives by quantum crystallography

Applications of 9-aminoacridine (9aa) and its derivatives span fields such as chemistry, biology, and medicine, including anticancer and antimicrobial activities. Protonation of such molecules can alter their bioavailability as weakly basic drugs like aminoacridines exhibit reduced solubility at high pH levels potentially limiting their effectiveness in patients with elevated gastric pH. In this study, we analyse the influence of protonation on the electronic characteristics of the molecular organic crystals of 9-aminoacridine. The application of quantum crystallography, including aspherical atom refinement, has enriched the depiction of electron density in the studied systems and non-covalent interactions, providing more details than previous studies. Our experimental results, combined with a topological analysis of the electron density and its Laplacian, provided detailed descriptions of how protonation changes the electron density distribution around the amine group and water molecule, concurrently decreasing the electron density at bond critical points of N/O-H bonds. Protonation also alters the molecular architecture of the systems under investigation. This is reflected in different proportions of the N⋯H and O⋯H intermolecular contacts for the neutral and protonated forms. Periodic DFT calculations of the cohesive energies of the crystal lattice, as well as computed interaction energies between molecules in the crystal, confirm that protonation stabilises the crystal structure due to a positive synergy between strong halogen and hydrogen bonds. Our findings highlight the potential of quantum crystallography in predicting crystal structure properties and point to its possible applications in developing new formulations for poorly soluble drugs.

General acid-mediated aminolactone formation using unactivated alkenes

Spirocyclic butyrolactones and butenolides are widespread structural motifs in bioactive substances. Despite their prevalence, a simple method ensuring their direct preparation from exocyclic alkenes, ideally in a late-stage context, remains elusive. Herein, we report direct aminolactone formation using unactivated alkenes which addresses this gap, employing cheap and readily available reactants. The method relies on the hijacking of a cationic aminoalkylation pathway and affords (spiro)aminolactones with excellent functional group tolerance and chemoselectivity. The synthetic versatility of the products is demonstrated through a range of transformations, notably exploiting stereospecific rearrangement chemistry to produce sterically congested scaffolds.

Electro-/photocatalytic alkene-derived radical cation chemistry: recent advances in synthetic applications

Alkene-derived radical cations are versatile reactive intermediates and have been widely applied in the construction of complex functionalized molecules and cyclic systems for chemical synthesis. Therefore, the synthetic application of these alkene-derived radical cations represents a powerful and green tool that can be used to achieve the functionalization of alkenes partially because the necessity of stoichiometric external chemical oxidants and/or hazardous reaction conditions is eliminated. This review summarizes the recent advances in the synthetic applications of the electro-/photochemical alkene-derived radical cations, emphasizing the key single-electron oxidation steps of the alkenes, the scope and limitations of the substrates, and the related reaction mechanisms. Using electrocatalysis and/or photocatalysis, single electron transfer (SET) oxidation of the CC bonds in the alkenes occurs, generating the alkene-derived radical cations, which sequentially enables the functionalization of translocated radical cations to occur in two ways: the first involves direct reaction with a nucleophile/radical or two molecules of nucleophiles to realize hydrofunctionalization, difunctionalization and cyclization; and the second involves the transformation of the alkene-derived radical cations into carbon-centered radicals using a base followed by radical coupling or oxidative nucleophilic coupling.

Hypervalent Iodine Mediated Oxidation Followed by Acetoxylation / Tosylation of α-Substituted Benzylamines Accessing to α-Acyloxy / Tosyloxy Ketones

An efficient and metal-free method has been developed for sequential oxidation followed by acetoxylation, tosylation of α-alkylbenzylamines for the synthesis of α-acyloxy / tosyloxy ketones by using hypervalent iodine (III)...

A desulphurization strategy for Sonogashira couplings by visible light/copper catalysis

We have developed a new copper-based photocatalyst, [(binap)(tpy)Cu]Cl, and applied it in the visible-light promoted Sonogashira coupling reactions.

Alkylsulfonium salts for the photochemical desulphurizative functionalization of heteroarenes

A metal-free organic photoredox-catalyzed alkylation of heteroarenes using alkylsulfonium salts as alkylation reagents has been developed.

C–H benzylation of quinoxalin-2(1H)-ones via visible-light riboflavin photocatalysis

An efficient visible light promoted riboflavin-catalyzed direct benzylation of substituted quinoxalin-2(1H)-ones for the synthesis of various C3-benzylated quinoxalin-2(1H)-one derivatives has been developed under mild conditions.

Decarboxylative Oxyacyloxylation of Propiolic Acids: Construction of Alkynyl-Containing α-Acyloxy Ketones

Novel decarboxylative oxyacyloxylation of propiolic acids has been developed. This reaction provides an efficient access to alkynyl-containing α-acyloxy ketones from readily available starting materials and exhibits significant functional group tolerance. Furthermore, oxyacyloxylation of terminal alkynes and aliphatic propiolic acids was also developed. A possible reaction mechanism is proposed based on mechanistic studies.

Light-driven selective aerobic oxidation of (iso)quinoliniums and related heterocycles

Selective C1–H/C4–H carbonylation of N-methylene iminium salts, catalyzed by visible-light photoredox and oxygen in the air, has been reported. A ruthenium complex acts as a chemical switch to conduct two different reaction pathways and to afford two different kinds of products. In the absence of the ruthenium complex, the Csp²–H bonds adjacent to the nitrogen atoms are oxidized to α-lactams by the N-methyleneiminium substrates themselves as photosensitizers. In the presence of the ruthenium complex, the oxidation reaction site of quinoliniums is switched to the C4 region, resulting in the formation of 4-quinolones. The use of two transformations directly introduces oxygen into the nitrogen heterocyclic skeletons under an air atmosphere.

The selective C1–H/C4–H carbonylation of N-methyleneiminium salts catalyzed by visible-light photoredox reactions and oxygen in the air has been reported.

Visible light-induced aerobic dioxygenation of α,β-unsaturated amides/alkenes toward selective synthesis of β-oxy alcohols using rose bengal as a photosensitizer

The first visible light-induced aerobic dioxygenation of alkenes for the selective synthesis of β-oxy alcohols was developed using non-toxic rose bengal as a photosensitizer.

Controllable synthesis of 2- and 3-aryl-benzomorpholines from 2-aminophenols and 4-vinylphenols

We present herein a method for the controllable synthesis of 3-aryl-benzomorpholine and 2-aryl-benzomorpholine cycloadducts via cross-coupling/annulation between electron-rich 2-aminophenols and 4-vinylphenols. Molecular oxygen was successfully used in the reaction as the terminal oxidant and the complete inversion of chemoselectivity was achieved by the adjustment of the solvents and bases at room temperature.

Recent Advances on Metal-Free, Visible-Light- Induced Catalysis for Assembling Nitrogen- and Oxygen-Based Heterocyclic Scaffolds

Heterocycles are important class of structures, which occupy a major space in the domain of natural and bioactive compounds. For this reason, development of new synthetic strategies for their controllable synthesis became of special interests. The development of novel photoredox systems with wide-range application in organic synthesis is particularly interesting. Organic dyes have been widely applied as photoredox catalysts in organic synthesis. Their low costs compared to the typical photocatalysts based on transition metals make them an excellent alternative. This review describes proceedings since 2015 in the area of application of metal-free, visible-light-mediated catalysis for assembling various heterocyclic scaffolds containing five- and six-membered rings bearing nitrogen and oxygen heteroatoms.

trans-Diastereoselective Syntheses of γ-Lactones by Visible Light-Iodine-Mediated Carboesterification of Alkenes

This study aims to develop an intermolecular lactonization reaction of alkenes with carbonyls mediated by visible light and molecular iodine. The one-step reaction involved the carboesterification of alkenes to produce the corresponding lactones in moderate to good yield. It was also revealed that it is possible to control the diastereoselectivity of the reaction by altering the base used and the reaction conditions. When water was added as a solvent, the reaction resulted in the formation of lactones with trans-selectivity. A mechanistic investigation was undertaken and it was found that the reaction requires the generation of an iodine radical from molecular iodine, driven by visible light irradiation, and proceeds via the formation of an iodine radical alkene adduct. The proposed reaction is an example of a rare-metal free intermolecular addition cyclization reaction, which is an environment-friendly chemical process that only uses molecular iodine. In addition, since diastereoselectivity was observed without the use of any specific reagents, the developed methodology is an example of a novel stereoselective transformation using only cost-effective reagents.

Photoorganocatalysis, small organic molecules and light in the service of organic synthesis: the awakening of a sleeping giant

Photocatalysis, the use of light to promote organic transformations, is a field of catalysis that has received limited attention despite existing for over 100 years. With the revolution of photoredox catalysis in 2008, the rebirth or awakening of the field of photoorganocatalysis has brought new ideas and reactions to organic synthesis. This review will focus on the sudden outburst of literature regarding the use of small organic molecules as photocatalysts after 2013. In particular, it will focus on acridinium salts, benzophenones, pyrylium salts, thioxanthone derivatives, phenylglyoxylic acid, BODIPYs, flavin derivatives, and classes of organic molecules as catalysts for the photocatalytic generation of C-C and C-X bonds.

Recent methods for the synthesis of α-acyloxy ketones

The present review provides a broad description of the methods reported for the synthesis of α-acyloxy ketones and some of their derivatives.

Recent advances in visible-light-driven organic reactions

In recent years, visible-light-driven organic reactions have been experiencing a significant renaissance in response to topical interest in environmentally friendly green chemical synthesis. The transformations using inexpensive, readily available visible-light sources have come to the forefront in organic chemistry as a powerful strategy for the activation of small molecules. In this review, we focus on recent advances in the development of visible-light-driven organic reactions, including aerobic oxidation, hydrogen-evolution reactions, energy-transfer reactions and asymmetric reactions. These key research topics represent a promising strategy towards the development of practical, scalable industrial processes with great environmental benefits.

Synthesis of carbonylated heteroaromatic compounds via visible-light-driven intramolecular decarboxylative cyclization of o-alkynylated carboxylic acids

An efficient strategy for the easy access to carbonylated heteroaromatic compounds has been developed via a visible-light-promoted intramolecular decarboxylative cyclization reaction of o-alkynylated carboxylic acids.

Photocatalytic Dehydrogenative Cross-Coupling of Alkenes with Alcohols or Azoles without External Oxidant

Direct cross-coupling between alkenes/R-H or alkenes/RXH is a dream reaction, especially without external oxidants. Inputting energy by photocatalysis and employing a cobalt catalyst as a two-electron acceptor, a direct C-H/X-H cross-coupling with H₂ evolution has been achieved for C-O and C-N bond formation. A new radical alkenylation using alkene as the redox compound is presented. A wide range of aliphatic alcohols-even long chain alcohols-are tolerated well in this system, providing a new route to multi-substituted enol ether derivatives using simple alkenes. Additionally, this protocol can also be used for N-vinylazole synthesis. Mechanistic insights reveal that the cobalt catalyst oxidizes the photocatalyst to revive the photocatalytic cycle.