Reductive Alkylation of Quinolines to N-Alkyl Tetrahydroquinolines Catalyzed by Arylboronic Acid

Facile synthesis of tetrahydroquinoline containing dithiocarbamate derivatives via one-pot sequential multicomponent reaction

An efficient sequential multi-component method for the synthesis of tetrahydroquinoline containing dithiocarbamates has been developed. This reaction involved a boronic acid-catalysed reduction of quinolines to tertrahydroquinolines, followed by nucleophilic addition reaction with carbon disulphide to form dithiocarbamic acids and subsequent S-arylation via external base-free Chan-Evans-Lam coupling in a one-pot operation. The methodology is compatible with a wide variety of functional groups and also useful in the late-stage functionalization of pharmaceuticals. The dual role of the boronic acid as a catalyst (in the reduction of quinolines) and as a reagent (in the S-arylation) has been demonstrated for the first time herein.

Emergent Organoboron Acid Catalysts

Organoboron acids are stable, organic-soluble Lewis acids with potential application as catalysts for a wide variety of chemical reactions. In this review, we summarize the utility of boronic and borinic acids, as well as boric acid, as catalysts for organic transformations. Typically, the catalytic processes exploit the Lewis acidity of trivalent boron, enabling the reversible formation of a covalent bond with oxygen. Our focus is on recent developments in the catalysis of dehydration, carbonyl condensation, acylation, alkylation, and cycloaddition reactions. We conclude that organoboron acids have a highly favorable prospectus as the source of new catalysts.

CsPbBr3 Quantum Dots Promoted Depolymerization of Oxidized Lignin via Photocatalytic Semi-Hydrogenation/Reduction Strategy

Due to the demanding depolymerization conditions and limited catalytic efficiency, enhancing lignin valorization remains challenging. Therefore, lowering the bond dissociation energy (BDE) has emerged as a viable strategy for achieving mild yet highly effective cleavage of bonds. In this study, a photocatalytic semi-hydrogenation/reduction strategy utilizing CsPbBr3 quantum dots (CPB-QDs) and Hantzsch ester (HEH2 ) as a synergistic catalytic system was introduced to reduce the BDE of Cβ -O-Ar, achieving effective cleavage of the Cβ -O-Ar bond. This strategy offers a wide substrate scope encompassing various β-O-4 model lignin dimers, preoxidized β-O-4 polymers, and native oxidized lignin, resulting in the production of corresponding ketones and phenols. Notably, this approach attained a turnover frequency (TOF) that is 17 times higher than that of the reported Ir-catalytic system in the photocatalytic depolymerization of the lignin model dimers. It has been observed via meticulous experimentation that HEH2 can be activated by CPB-QDs via single electron transfer (SET), generating HEH2 ⋅+ as a hydrogen donor while also serving as a hole quencher. Moreover, HEH2 ⋅+ readily forms an active transition state with the substrates via hydrogen bonding. Subsequently, the proton-coupled electron transfer (PCET) from HEH2 ⋅+ to the carbonyl group of the substrate generates a Cα ⋅ intermediate.

HTE- and AI-assisted development of DHP-catalyzed decarboxylative selenation

1,4-Dihydropyridine (DHP) derivatives play key roles in biology, but are rarely used as catalysts in synthesis. Here, we developed a DHP derivative-catalyzed decarboxylative selenation reaction that showed a broad substrate scope, with the assistance of high-throughput experimentation (HTE) and artificial intelligence (AI). The AI-based model could identify the key structural features and give accurate prediction of unseen reactions (R² = 0.89, RMSE = 9.0%, and MAE = 6.3%). Our work not only developed the catalytic applications of DHP derivatives, but also demonstrated the power of the combination of HTE and AI to advance chemical synthesis.

[4-(3,4-Dimethoxyphenyl)-3,6-dimethyl-2-phenyl-3,4-dihydroquinolin-1(2H)-yl)](furan-2-yl)methanone

A N-(2,4-diaryltetrahydroquinolin-1-yl) furan-2-carboxamide derivative, [4-(3,4-dimethoxyphenyl)-3,6-dimethyl-2-phenyl-3,4-dihydroquinolin-1(2H)-yl)](furan-2-yl)methanone, was synthesized in a two-step procedure from p-toluidine, benzaldehyde, and trans-methyl-isoeugenol as commercial starting reagents through a sequence of Povarov cycloaddition reaction/N-furoylation processes. The structure of the compound was fully characterized by IR, 1H, 13C-NMR, and X-ray diffraction data. Such types of derivatives are known as relevant therapeutic agents exhibiting potent anticancer, antibacterial, antifungal, anti-inflammatory, and immunological modulator properties.