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Irradiation of vinyl and aryl azides with visible light in the presence of Ru photocatalysts results in the formation of reactive nitrenes, which can undergo a variety of CN bond-forming reactions. The ability to use low-energy visible light instead of UV in the photochemical activation of azides avoids competitive photodecomposition processes that have long been a significant limitation on the synthetic use of these reactions. [ABSTRACT FROM AUTHOR]

We have developed a photocatalytic reduction of nitroarenes as an efficient, chemoselective route to biologically important N-phenyl hydroxamic acid scaffolds. Optimal conditions call for 2.5 mol% of a ruthenium photocatalyst, visible light irradiation, and a dihydropyridine terminal reductant. Because of the mild nature of the visible light activation, functional groups that might be sensitive to other non-photochemical reduction methods are easily tolerated. [ABSTRACT FROM AUTHOR]

Tehshik P. Yoon is a Professor of Chemistry at the University of Wisconsin–Madison (USA). He is a current member of the ChemPhotoChem Editorial Board. [ABSTRACT FROM AUTHOR]

One of the most active current areas of chemical research is centered on how to synthesize handed (chiral) compounds in a selective manner, rather than as mixtures of mirror-image forms (enantiomers) with different three-dimensional structures (stereochemistries). Nature points the way in this endeavor: different enantiomers of a given biomolecule can exhibit dramatically different biological activities, and enzymes have therefore evolved to catalyze reactions with exquisite selectivity for the formation of one enantiomeric form over the other. Drawing inspiration from these natural catalysts, chemists have developed a variety of synthetic small-molecule catalysts that can achieve levels of selectivity approaching, and in some cases matching, those observed in enzymatic reactions. [ABSTRACT FROM AUTHOR]

The sole method available for the photocycloaddition of unconjugated aliphatic alkenes is the Cu‐catalyzed Salomon–Kochi reaction. The [Cu(OTf)]2⋅benzene catalyst that has been standard in this reaction for many decades, however, is air‐sensitive, prone to photodecomposition, and poorly reactive towards sterically bulky alkene substrates. Using bench‐stable precursors, an improved catalyst system with superior reactivity and photostability has been designed, and it offers significantly expanded substrate scope. The utility of this new catalyst for the preparation of sterically crowded cyclobutane structures is highlighted through the preparation of the cores of the natural products sulcatine G and perforatol. [ABSTRACT FROM AUTHOR]

A review of the article discussing a strategy for photochemical reactions using visible light by H. Huo and colleagues, which appeared in the periodical "Nature" on November 6, 2014 issue, is presented.

The article provides information on the effectiveness of iron salts as catalysts for oxaziridine-mediated oxyamination. It states that transition-metal salts screening was conducted in the study. Findings show that both FeBr3 and Fe(acac)3 generated the regioisomer 2 from the oxaziridine 1a and 4-methylstyrene (eq 1). It also reveals the availability of 1,2-aminoalcohols in regioisomeric form by vicinal oxyamination of olefins.

A preview is presented of the research article "Solar Synthesis: Prospects in Visible Light Photocatalysis," by Danielle M. Schultz and Tehshik P. Yoon, which is available at the web address http://dx.doi.org/10.1126/science.1239176 as of February 28, 2014.

Abstract: We report that is an excellent sensitizer for the photooxygenation of aryl cyclopropanes upon irradiation with visible light. The effectiveness of this photocatalyst enables the synthesis of a range of five-membered endoperoxides in excellent yield with quite low (0.5 mol %) catalyst loadings even when standard household light sources are utilized. [Copyright &y& Elsevier]

Abstract: We report an oxaziridine-mediated enantioselective aminohydroxylation of olefins catalyzed by a chiral copper(II) bis(oxazoline) complex. A variety of styrenic olefins undergo efficient aminohydroxylation with excellent regioselectivity and synthetically useful levels of enantioselectivity (up to 84% ee). The reaction can be conducted on multi-gram scale with as little as 2mol% of the copper(II) catalyst. Hydrolysis of the resulting 1,3-oxazolines under acidic conditions produces N-sulfonyl amino alcohols that can be purified by recrystallization to afford very high levels of enantioselectivity. [Copyright &y& Elsevier]

N-Sulfonyl oxaziridines are susceptible to electrophilic activation using copper(II) catalysts and react with styrenes under these conditions to provide 1,3-oxazolidines in a formal aminohydroxylation of the alkene. We propose a two-step mechanism involving a cationic intermediate to account for the rate differences and regioselectivities observed using a variety of styrenes. In accord with our hypothesis, aminohydroxylations of a range of substrates bearing electron-stabilizing groups are successful, and 1,3-dienes are particularly good substrates for copper(II)-catalyzed aminohydroxylation. Reactions of unsymmetrical dienes provide good to excellent olefin selectivity, the sense and magnitude of which can be rationalized upon consideration of the stability of the cationic intermediates suggested by our mechanism. Diastereoselective synthesis of a diverse range of densely functionalized structures can be achieved by polyfunctionalization of dienes using aminohydroxylation as a key complexity-increasing step. [ABSTRACT FROM AUTHOR]

We report that an NMR spectrometer equipped with a high‐power LED light source can be used to study a fast enantioselective photocatalytic [2+2] cycloaddition. While traditional ex situ applications of NMR provide considerable information on reaction mechanisms, they are often ineffective for observing fast reactions. Recently, motivated by renewed interest in organic photochemistry, several approaches have been reported for in situ monitoring of photochemical reactions. These previously disclosed methods, however, have rarely been applied to rapid (<5 min) photochemical reactions. Furthermore, these approaches have not previously been used to interrogate the mechanisms of photocatalytic energy‐transfer reactions. In the present work, we describe our experimental setup and demonstrate its utility by determining a phenomenological rate law for a model photocatalytic energy‐transfer cycloaddition reaction. [ABSTRACT FROM AUTHOR]

The article presents a new means for the catalyzed formation of Lewis acid, as well as cycloaddition of a differently inaccessible N-nosyl nitrones. These nitrones have the ability to generate 1,2-isoxazolidines that can be deprotected in meek considerations. Details of the study are also explained and provided for in the article.

Relatively few catalytic systems are able to control the stereochemistry of electronically excited organic intermediates. Here we report the discovery that a chiral Lewis acid complex can catalyze triplet energy transfer from an electronically excited photosensitizer.We applied this strategy to asymmetric [2 + 2] photocycloadditions of 2′-hydroxychalcones, using tris(bipyridyl) ruthenium(II) as a sensitizer. A variety of electrochemical, computational, and spectroscopic data rule out substrate activation by means of photoinduced electron transfer and instead support a mechanism in which Lewis acid coordination dramatically lowers the triplet energy of the chalcone substrate.We expect that this approach will enable chemists to more broadly apply their detailed understanding of chiral Lewis acid catalysis to stereocontrol in reactions involving electronically excited states. [ABSTRACT FROM AUTHOR]

In contrast to the wealth of catalytic systems that are available to control the stereochemistry of thermally promoted cycloadditions, few similarly effective methods exist for the stereocontrol of photochemical cycloadditions. A major unsolved challenge in the design of enantioselective catalytic photocycloaddition reactions has been the difficulty of controlling racemic background reactions that occur by direct photoexcitation of substrates while unbound to catalyst. Here, we describe a strategy for eliminating the racemic background reaction in asymmetric [2 + 2] photocycloadditions of α,β-unsaturated ketones to the corresponding cyclobutanes by using a dual-catalyst system consisting of a visible light-absorbing transition-metal photocatalyst and a Stereocontrolling Lewis acid cocatalyst. The independence of these two catalysts enables broader scope, greater stereochemical flexibility, and better efficiency than previously reported methods for enantioselective photochemical cycloadditions. [ABSTRACT FROM AUTHOR]

Abstract: We have discovered a photocatalytic intramolecular hetero-Diels–Alder reaction of tethered bis(enones). This transformation involves the intermediacy of an enone radical anion and constitutes the formal coupling of an electron-deficient heterodiene with an electronically mismatched enone dienophile. The diastereoselectivity and regioselectivity of the process are high, and the dihydropyran products are amenable to a variety of synthetically useful transformations. [Copyright &y& Elsevier]

The article focuses on the oxaziridine-intermediated intramolecular amination of 3-hybridized C-H bonds in 2009. Various oxidations of hydrocarbon are among the capabilities that can be done by oxaziridines. It states that oxaziridines that contain robust electron-withdrawing substituents are capable of oxidizing C-H bonds.

The article discusses the study which develops new strategies for efficient visible light photocatalysis of synthetic transformations. It examines the [2+2] cycloaddition of bis(enone) 1 for the investigations into visible light photocatalysis. Key information on the methodologies and results is further presented.

The di-π-methane (DPM) rearrangement is an important organic photorearrangement that converts 1,4-diene-containing compounds to vinyl cyclopropanes, often resulting in extensive, synthetically valuable restructuring of the substrate's carbon framework. We investigated the influence of Lewis and Brønsted acids on the DPM rearrangement of dibenzobarrelenes. These studies have culminated in the identification of a dual chiral Brønsted acid-iridium photosensitizer system that enables the first highly enantioselective catalytic all-carbon DPM rearrangement.

Bicyclo[2.1.1]hexanes have emerged as valuable scaffolds for the design of new pharmaceutical and agrochemical active ingredients. These structures can be efficiently synthesized via [2π + 2σ] photocycloadditions; however, control over the absolute stereochemistry of these strain-releasing reactions has remained challenging. Herein, we demonstrate that Brønsted acid catalyzed chromophore activation of C -acyl imidazoles enables highly enantioselective [2π + 2σ] photocycloadditions. Because this approach is agnostic to the identity of the coupling partner, the same strategy can be used to synthesize several other medicinally relevant strained small-ring structures.

A new reaction swaps an oxygen for a nitrogen in structurally complex molecules.

We report a deep learning-based approach to accurately predict the emission spectra of phosphorescent heteroleptic [Ir( C ∧ N ${{\rm{C}}^\wedge {\rm{N}}}$ ) 2 ( N ∧ N ${{\rm{N}}^\wedge {\rm{N}}}$ )] + complexes, enabling the rapid discovery of novel Ir(III) chromophores for diverse applications including organic light-emitting diodes and solar fuel cells. The deep learning models utilize graph neural networks and other chemical features in architectures that reflect the inherent structure of the heteroleptic complexes, composed of C ∧ N ${{\rm{C}}^\wedge {\rm{N}}}$ and N ∧ N ${{\rm{N}}^\wedge {\rm{N}}}$ ligands, and are thus geared towards efficient training over the dataset. By leveraging experimental emission data, our models reliably predict the full emission spectra of these complexes across various emission profiles, surpassing the accuracy of conventional DFT and correlated wavefunction methods, while simultaneously achieving robustness to the presence of imperfect (noisy, low-quality) training spectra. We showcase the potential applications for these and related models for in silico prediction of complexes with tailored emission properties, as well as in "design of experiment" contexts to reduce the synthetic burden of high-throughput screening. In the latter case, we demonstrate that the models allow us to exploit a limited amount of experimental data to explore a wide range of chemical space, thus leveraging a modest synthetic effort., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

The truxillates constitute a large class of dimeric natural products featuring a central, highly substituted cyclobutane core. In principle, these structures could be efficiently synthesized via [2 + 2] photocycloaddition. However, the difficulty in controlling the high-energy electronically excited reactive intermediates in the solution state can lead to poor regio- and diastereocontrol. This has limited the use of photocycloaddition methodology toward the synthesis of this important class of natural products. Herein, we demonstrate that acid-controlled precipitation of C -acyl imidazoles promotes a highly selective solid-state photocycloaddition, and the products of this reaction can be quickly transformed into truxillate natural products.

The Paternò-Büchi reaction is the [2 + 2] photocycloaddition of a carbonyl with an alkene to afford an oxetane. Enantioselective catalysis of this classical photoreaction, however, has proven to be a long-standing challenge. Many of the best-developed strategies for asymmetric photochemistry are not suitable to address this problem because the interaction of carbonyls with Brønsted or Lewis acidic catalysts can alter the electronic structure of their excited state and divert their reactivity toward alternate photoproducts. We show herein that a triplet rebound strategy enables the stereocontrolled reaction of an excited-state carbonyl compound in its native, unbound state. These studies have resulted in the development of the first highly enantioselective catalytic Paternò-Büchi reaction, catalyzed by a novel hydrogen-bonding chiral Ir photocatalyst.