Advanced Synthesis & Catalysis最新文献

Catalytic processes utilizing air as an environmentally benign oxidizing agent and acid catalysts offer significant advantages in converting renewable or sustainable carbohydrate feedstocks into high-value chemical compounds. Herein, a remarkably efficient and innovative Brønsted acid-catalyzed system has been developed, utilizing air as the sole oxidant, completely devoid of transition metals or costly oxidizing reagents. The system enables oxidative C−C/H activation and N-formamidation of amine and dextrose with notable efficiency synthesis of a diverse array of formamides while achieving impressive turnover numbers (TON = 91,455). Labeling studies have demonstrated that the carbon atom in the aldehyde group originates from the C1 position of dextrose, the hydrogen atoms are derived from the C−H bonds position within the dextrose skeleton, the H atom in the amide (NH) group originates from a hydroxyl group of dextrose, and the oxygen atom is derived from atmospheric O₂. Mechanistic investigations have revealed that acidic conditions significantly promote the oxidation of dextrose by molecular oxygen.

A visible-light-driven, photocatalyst-free 6π-photocyclization of N-substituted dieneamines has been developed. Various polysubstituted cyanodihydropyrroles and cyanopyrroles were constructed in good-to-excellent yields under nitrogen or air atmosphere. This novel strategy features formal hydroalkenylation, divergent synthesis, excellent regioselectivity, wide functional group tolerance, and operational convenience. Mechanistic studies suggest that both the 1,4-H shift of the diradical intermediate and the deprotonation/protonation processes may be involved in the transformation.

Accurately controlling chemoselectivity is a challenging goal in the synthesis of important pharmaceuticals, pesticides, and functional materials. In this work, we report the first example of chemoselective oxidation of benzylamine to producing benzonitriles, benzaldehydes, and imines, respectively, through the regulation of reaction solvent and additive under 400 nm light irradiation using Rose Bengal as a photocatalyst. The organic compounds are successfully used as photocatalysts for the first time in the oxidative cyanation of benzylamine in photocatalytic systems. Control experiments, mechanism studies, and density functional theory calculations revealed that the reaction undergoes a photolytical single-electron transfer process, and the cleavage of the benzylic CH bond is the rate-determining step in the reaction. Noted that the active species of Rose Bengal-acetamidine hydrochloride was found and structurally verified by X-ray single-crystal diffraction analysis.

Considering the explosive characteristics of hydrogen and the importance of preventing leakage, achieving controlled low-temperature combustion ensures both environmental safety and operational stability. Low-temperature catalytic combustion provides an effective solution to reduce hazardous pollutant formation during the hydrogen reaction. In this article, a spinel-based catalyst modified by partial substitution with transition metals (M) is prepared and doped with bimetallic Pt:Cu to enhance hydrogen catalytic combustion. The doped composite spinel Co_1-xM_xAl₂O₄ catalyst, where M represents Fe, Ti, and Mn, is synthesized using wet impregnation followed by a polyethylene glycol (PEG)-assisted sol–gel doping method to obtain a PtCu/Co_0.8Fe_0.2Al₂O₄ catalyst. Combining performance testing and material characterization, Fe-modified spinel exhibited a larger specific surface area of 31.63 m²/g compared to 30.46 m²/g, lowered activation energy from 57.8 to 46.9 kJ/mol, achieving a T₉₀ at 349°C compared to 374.3°C for original CoAl₂O₄. Meanwhile, the bimetallic Pt 1%-Cu 4%/Co_0.8Fe_0.2Al₂O₄ catalyst exhibits excellent activity with T₅₀ at 37.07°C and T₉₀ at 43.34°C, attributed to a minimum activation energy of 32 kJ/mol. The synergistic effect at 4% and 5% Cu loadings is supported by high metal dispersion and structural stability of the Fe-modified spinel matrix, enabling room-temperature combustion initiation. This enhanced catalytic activity results from strong Pt–Cu bimetallic interactions, promoting efficient hydrogen dissociation while increasing oxygen vacancy formation and lattice oxygen mobility, as revealed by X-ray photoelectron spectroscopy, temperature-programed reduction, and thermogravimetric analysis. Overall, the enhanced low-temperature hydrogen combustion performance is comparable to standard precious metal catalysts, referencing the multimetallic effect on fuel utilization efficiency.

Terpenes represent the most abundant class of natural products, with monoterpenes and their hydroxylated derivatives being highly sought after in the flavor and fragrance as well as pharmaceutical industry. However, the selective oxyfunctionalization of these compounds remains challenging. Cumene dioxygenase (CDO) from Pseudomonas fluorescens IP01 has emerged as a promising biocatalyst for monoterpene hydroxylation, though achieving precise regioselectivity control has proven nontrivial. Here, we report the successful engineering of CDO to achieve exceptional regioselective control over this challenging substrate class. The identification of L333A as an important generalist variant proved fundamental, not only enhancing product formation but also opening the way for the conversion of novel monoterpene substrates. Through iterative site-saturation mutagenesis, we developed enhanced variants which achieved up to 90% selectivity for (R)- and (S)-limonene-10-ol as well as up to 67% for (R)- and (S)-perillyl alcohol while exhibiting additionally improved total product formation. Furthermore, engineered variants significantly broadened the substrate scope of CDO, enabling hydroxylation of all four pinene isomers as well as the monoterpenoids geraniol and (−)-linalool with selectivities of up to 99%. In summary, this work demonstrates the remarkable potential of tailored Rieske oxygenases for the sustainable production of valuable hydroxylated monoterpenes.

We selectively synthesized a less explored furan-2-ylmethylmethyl carbonate (FMMC), a potential green solvent and fuel additive via carboxymethylation of furfuryl alcohol with dimethyl carbonate. A defect-engineered UiO-66 MOF catalyst was employed for this transformation, and its activity was benchmarked against conventional catalysts such as H-ZSM-5, H-Beta, and Amberlyst-15. The nature of the active sites instrumental in obtaining high FMMC selectivity was emphasized by the variation in turnover numbers. The in situ approach of tailoring missing linker defects in the UiO-66 MOF was achieved with monocarboxylic acid modulators, formic acid and acetic acid. The catalysts were comprehensively characterized for the structural properties by PXRD, N₂ sorption, and FESEM, and the intrinsic active sites were investigated with techniques such as EPR, FTIR, TGA, and acid–base titrations. The defective UiO-66 MOF demonstrated superior catalytic activity owing to the presence of a higher number of weak Brönsted acidic sites. The selective masking of Brönsted and Lewis acidic sites were studied by treating it with 2,6-lutidine and KSCN respectively and their effect on the catalytic activity was examined. A Central Composite Design (CCD) model was designed to obtain the high FMMC yield under optimized conditions. The catalyst gave 87.3% furfuryl alcohol conversion and 95.2% FMMC selectivity. The leaching and recyclability experiments showed that the catalyst was truly heterogeneous, and it was recyclable up to five consecutive cycles. The spent catalyst was thoroughly characterized to understand the stability and structural and intrinsic properties.

Metal hydride hydrogen atom transfer-mediated intramolecular cascade radical cyclization of vinylogous N-alkoxycarbamate is described for the stereoselective synthesis of 1,2-oxazinane and 1,2-oxazepane derivatives. This strategy relies on 6-exo-trig and 7-exo-trig radical cyclizations of alkenyl vinylogous N-alkoxycarbamate. The influence of nitrogen protecting groups on the efficiency and outcome of the radical cyclization was systematically investigated. Furthermore, the developed methodology enables the construction of structurally unique oxa-aza-spirocyclic frameworks, expanding the synthetic utility of this radical cascade approach.

The stereoselective disulfidation of alkynes remains a compelling yet challenging transformation in organic chemistry. In this study, we report a visible light-induced radical disulfidation of alkynes for the synthesis of (E)-vinyl sulfides. In contrast to previous methods that proceed through nucleophilic or metal-mediated alkyne insertion pathways, this protocol operates via a rarely explored radical mechanism under mild, metal-free conditions. A broad range of alkynes and thiols are well tolerated, affording (E)-vinyl sulfides selectively. This one-pot strategy provides a green and atom-economical approach to stereodefined (E)-vinyl sulfide scaffolds.

A novel copper-catalyzed protocol is discovered for the synthesis of quinoxalines through the direct coupling of β,β-disubstituted nitroalkenes and o-phenylenediamines. The cascade transformation proceeds via a mechanistically intriguing pathway involving allylic CH bond oxidation followed by cyclocondensation. Remarkably, o-phenylenediamines are proposed to play a dual role, serving not only as conventional condensation partners but also as essential ligands that facilitate the copper-catalyzed oxidative transformation.

Development of new asymmetric radical reactions is of significant interest to the synthetic community. In this article, we describe a chiral Brønsted acid catalyzed enantioselective α-oxidation of ketones carrying heteroaromatic templates using TEMPO and a metal oxidant. The methodology provides access to α-aminoxylated ketones in high yields and good enantioselectivities.