Chemoselective Nucleophilic Functionalizations of Aromatic Aldehydes and Acetals via Pyridinium Salt Intermediates

Artificial Photosynthases: Single-Chain Nanoparticles with Manifold Visible-Light Photocatalytic Activity for Challenging "in Water" Organic Reactions

Photocatalyzed reactions of organic substances in aqueous media are challenging transformations, often because of scarce solubility of substrates and catalyst deactivation. Herein, we report single-chain nanoparticles, SCNPs, capable of efficiently catalyzing four different "in water" organic reactions by employing visible light as the only external energy source. Specifically, we decorated a high-molecular-weight copolymer, poly(OEGMA300-r-AEMA), with iridium(III) cyclometalated complex pendants at varying content amounts. The isolated functionalized copolymers demonstrated self-assembly into noncovalent, amphiphilic SCNPs in water, which enabled efficient visible-light photocatalysis of two reactions unprecedentedly reported in water, namely, [2 + 2] photocycloaddition of vinyl arenes and α-arylation of N-arylamines. Additionally, aerobic oxidation of 9-substituted anthracenes and β-sulfonylation of α-methylstyrene were successfully carried out in aqueous media. Hence, by merging metal-mediated photocatalysis and SCNPs for the fabrication of artificial photoenzyme-like nano-objects─i.e., artificial photosynthases (APS)─our work broadens the possibilities for performing challenging "in water" organic transformations via visible-light photocatalysis.

Theoretical Analysis of Selectivity Differences in Ketoreductases toward Aldehyde and Ketone Carbonyl Groups

Lactobacillus kefir alcohol dehydrogenase (LkADH) and ketoreductase from Chryseobacterium sp. CA49 (ChKRED12) exhibit different chemoselectivity and stereoselectivity toward a substrate with both keto and aldehyde carbonyl groups. LkADH selectively reduces the keto carbonyl group while retaining the aldehyde carbonyl group, producing optically pure R-alcohols. In contrast, ChKRED12 selectively reduces the aldehyde group and exhibits low reactivity toward ketone carbonyls. This study investigated the structural basis for these differences and the role of specific residues in the active site. Molecular dynamics (MD) simulations and quantum chemical calculations were used to investigate the interactions between the substrate and the enzymes and the essential cause of this phenomenon. The present study has revealed that LkADH and ChKRED12 exhibit significant differences in the structure of their respective active pockets, which is a crucial determinant of their distinct chemoselectivity toward the same substrate. Moreover, residues N89, N113, and E144 within LkADH as well as Q151 and D190 within ChKRED12 have been identified as key contributors to substrate stabilization within the active pocket through electrostatic interactions and van der Waals forces, followed by hydride transfer utilizing the coenzyme NADPH. Furthermore, the enantioselectivity mechanism of LkADH has been elucidated using quantum chemical methods. Overall, these findings not only provide fundamental insights into the underlying reasons for the observed differences in selectivity but also offer a detailed mechanistic understanding of the catalytic reaction.

Competitive tetrel bond and hydrogen bond in benzaldehyde-CO2: characterization via rotational spectroscopy

The rotational spectrum of the 1 : 1 benzaldehyde-CO₂ complex has been investigated using pulsed-jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations. Two isomers, both characterized by one C⋯O tetrel bond (n → π* interaction) and one C-H⋯O hydrogen bond (n → σ* interaction), have been observed in the pulsed jet. Competition between the tetrel bond and the hydrogen bond has been disclosed by natural bond orbital analysis: isomer I is characterized by one dominating OC_CO2⋯O tetrel bond (12.6 kJ mol^-1) and a secondary (C-H)_formyl⋯O hydrogen bond (2.2 kJ mol^-1); by contrast, in isomer II the (C-H)_phenyl⋯O hydrogen bond (7.6 kJ mol^-1) becomes the dominant bond, while the OC_CO2⋯O tetrel bond (5.8 kJ mol^-1) becomes much weaker with respect to that of isomer I. Using intensity measurements the relative population ratio of the two isomers was estimated to be N_I/N_II ≈ 2/1.

Homologation of Alkyl Acetates, Alkyl Ethers, Acetals, and Ketals by Formal Insertion of Diazo Compounds into a Carbon–Carbon Bond

Homologation of alkyl acetates, alkyl ethers, acetals, and ketals was accomplished via formal insertion of diazo esters into carbon–carbon σ-bonds. The combined Lewis acid InI3 with Me3SiBr catalyzed the homologation of alkyl acetates and alkyl ethers. That of acetals and ketals was catalyzed solely by the use of InBr3. The key point of the homologation mechanism is that the indium-based Lewis acids have the appropriate amount of Lewis acidity to achieve both the abstraction and release of leaving groups. The abstraction of a leaving group by an indium-based Lewis acid and the electrophilic addition of carbocation or oxonium intermediates to diazo esters followed by the rearrangement of carbon substituents provide the corresponding cation intermediates. Finally, the leaving group that is captured by the Lewis acid bonds with cation intermediates to furnish the homologated products.

A Magnetically Recyclable Palladium-Catalyzed Formylation of Aryl Iodides with Formic Acid as CO Source: A Practical Access to Aromatic Aldehydes

A magnetically recyclable palladium-catalyzed formylation of aryl iodides under CO gas-free conditions has been developed by using a bidentate phosphine ligand-modified magnetic nanoparticles-anchored­ palladium(II) complex [2P-Fe3O4@SiO2-Pd(OAc)2] as catalyst, yielding a wide variety of aromatic aldehydes in moderate to excellent yields. Here, formic acid was employed as both the CO source and the hydrogen donor with iodine and PPh3 as the activators. This immobilized palladium catalyst can be obtained via a simple preparative procedure and can be facilely recovered simply by using an external magnetic field, and reused at least 9 times without any apparent loss of catalytic activity.

Flavin Nitroalkane Oxidase Mimics Compatibility with NOx/TEMPO Catalysis: Aerobic Oxidization of Alcohols, Diols, and Ethers

Biomimetic flavin organocatalysts oxidize nitromethane to formaldehyde and NO_x-providing a relatively nontoxic, noncaustic, and inexpensive source for catalytic NO₂ for aerobic TEMPO oxidations of alcohols, diols, and ethers. Alcohols were oxidized to aldehydes or ketones, cyclic ethers to esters, and terminal diols to lactones. In situ trapping of NO_x and formaldehyde suggest an oxidative Nef process reminiscent of flavoprotein nitroalkane oxidase reactivity, which is achieved by relatively stable 1,10-bridged flavins. The metal-free flavin/NO_x/TEMPO catalytic cycles are uniquely compatible, especially compared to other Nef and NO_x-generating processes, and reveal selectivity over flavin-catalyzed sulfoxide formation. Aliphatic ethers were oxidized by this method, as demonstrated by the conversion of (-)-ambroxide to (+)-sclareolide.

Aggregation-induced emission supramolecular organic framework (AIE SOF) gels constructed from tri-pillar[5]arene-based foldamer for ultrasensitive detection and separation of multi-analytes

In this study, a novel aggregation-induced emission supramolecular organic framework (AIE SOF) with ultrasensitive response, termed FSOF, was constructed using a tri-pillar[5]arene-based foldamer. Interestingly, benefiting from the noise signal shielding properties of FSOF as well as the competition between the cationπ and ππ interactions, the FSOF shows an ultrasensitive response for multi-analytes, such as Fe3+, Hg2+ and Cr3+. The limits of detection (LODs) of the FSOF for Fe3+, Hg2+ and Cr3+ are in the range of 9.40 × 10-10-1.86 × 10-9. More importantly, the xerogel of FSOF exhibits porous mesh structures, which could effect high-efficiency separation above metal ions from their aqueous solution, with adsorption percentages in the range 92.39-99.99%. In addition, by introducing metal ions into the FSOF, a series of metal ions coordinated supramolecular organic frameworks (MSOFs) were successfully constructed. Moreover, MSOFs show selective fluorescence "turn on" ultrasensitive detection CN- (LOD = 2.12 × 10-9) and H2PO4- (LOD = 1.78 × 10-9). This is a novel approach to construct SOFs through a tri-pillar[5]arene-based foldamer, and also provides a new way to achieve ultrasensitive detection and high-efficiency separation.