A visible-light-enabled selective oxidation of alcohols to aldehydes has been developed under transitionmetal-free conditions. Utilizing eosin Y as the direct hydrogen-atom transfer (HAT) photocatalyst and molecular oxygen as the terminal oxidant, both aromatic and aliphatic aldehydes could be obtained in moderate to good yields. Using this approach, various quinazolinones, including two real drug molecules, were easily synthesized from the corresponding o-aminobenzamides and alcohols. Scheme 1. Visible-light-enabled selective oxidation of alcohols to aldehydes and synthesis of quinazolinones from alcohols and o-aminobenzamides.
Employing a two‐dimensional covalent organic framework as the reusable solar photosensitizer, the sunlight‐driven aerobic oxidative construction of a nitrogen‐sulfur bond has been achieved. 3,5‐Disubstituted 1,2,4‐thiadiazoles are smoothly prepared in water by using this procedure. Furthermore, a radical mechanism with a sunlight‐promoted single electron transfer (SET) process is proposed for this transformation.
Mimicking the active site and the substrate binding cavity of the enzyme to achieve specificity in catalytic reactions is an essential challenge. Herein, porous coordination cages (PCCs) with intrinsic cavities and tunable metal centers have proved the regulation of reactive oxygen species (ROS) generating pathways as evidenced by multiple photo-induced oxidations. Remarkably, in the presence of the Zn 4 -μ 4 -O center, PCC converted dioxygen molecules from triplet to singlet excitons, whereas the Ni 4 -μ 4 -O center promoted the efficient dissociation of electrons and holes to conduct electron transfer towards substrates. Accordingly, the distinct ROS generation behavior of PCC-6-Zn and PCC-6-Ni enables the conversion of O 2 to 1 O 2 and O 2 *À , respectively. In contrast, the Co 4 -μ 4 -O center combined the 1 O 2 and O 2 *Àtogether to generate carbonyl radicals, which in turn reacted with the oxygen molecules. Harnessing the three oxygen activation pathways, PCC-6-M (M = Zn/Ni/Co) display specific catalytic activities in thioanisole oxidation (PCC-6-Zn), benzylamine coupling (PCC-6-Ni), and aldehyde autoxidation (PCC-6-Co). This work not only provides fundamental insights into the regulation of ROS generation by a supramolecular catalyst but also demonstrates a rare example of achieving reaction specificity through mimicking natural enzymes by PCCs.
H 2 O 2 detection is closely relevant to human health; however, most of the H 2 O 2 probes suffer from low accuracy and sensitivity because of the aggregating nature of solid sensors. In contrast, a mixed-matrix membrane (MMM) with high processability and flexibility is a suitable H 2 O 2 probe to overcome these drawbacks. Herein, we fabricated MOF-based MMMs by using a robust UiO-66-(COOH) 2 with carboxylate-chelating moieties, which were utilized for binding Fe (II) metal centers. The Fe (II)-immobilized MOF-MMM involved in a Fenton reaction when treated with H 2 O 2 , exhibiting a fluorescence turn-on property. Compared to the bulk-state MOF powder, the MOF-MMM sensor showed much-improved sensitivity (detection limit down to 0.0215 μM) because of the uniform dispersion of the probe and a sufficient contact with the analyte. This MOF-MMM sensor combinedly exhibited a turn-on fluorescence response and outstanding sensing properties with flexibility and processability, providing a novel platform suitable for practical sensing applications.
A simple and practical method for the one‐pot synthesis of 3‐aryl‐5‐amino‐1,2,4‐thiadiazoles from imidates and thioureas has been developed. The protocol proceeds through sequential base‐mediated nucleophilic addition‐elimination reactions and an I2‐mediated oxidative coupling for the N–S bond formation. The approach employes readily available and nontoxic substrates and a simple workup to provide 3‐aryl‐5‐amino‐1,2,4‐thiadiazoles that have a free or substituted amino group.
A direct strategy for the selective
synthesis of 3-acyl-1,2,4-oxadiazoles
from alkynes and nitriles has been developed under iron(III) nitrate-mediated
conditions. The mechanism includes three sequential procedures: iron(III)
nitrate-mediated nitration of alkynes leads to α-nitroketones,
dehydration of α-nitroketones provides the nitrile oxides, and
1,3-dipolar cycloaddition of nitrile oxides with nitriles produces
3-acyl-1,2,4-oxadiazoles under iron-mediated conditions. Iron(III)
nitrate plays dual roles in the nitration of alkynes and the activation
of nitriles, while the formation of pyrimidine/isoxazole byproducts
can be efficiently inhibited.
One of the hallmarks of multicomponent metal–organic
frameworks
(MOFs) is to finely tune their active centers to achieve product selectivity.
In particular, obtaining bimetallic MOF hollow structures with precisely
tailored redox centers under the same topology is still challenging
despite a recent surge of such efforts. Herein, we present an engineering
strategy named “cluster labilization” to generate hierarchically
porous MOF composites with hollow structures and tunable active centers.
By partially replacing zirconium with cerium in the hexanuclear clusters
of UiO-66, unevenly distributed yolk–shell structures (YSS)
were formed. Through acid treatment or annealing of the YSS precursor,
single-shell hollow structures (SSHS) or double-shell hollow structures
(DSHS) can be obtained, respectively. The active centers in SSHS and
DSHS differ in their species, valence, and spatial locations. More
importantly, YSS, SSHS, and DSHS with distinct active centers and
microenvironments exhibit tunable catalytic activity, reversed selectivity,
and high stability in the tandem reaction and the photoreaction.
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