The alkoxy radicals that are derived from cyclic hemiacetals have been generated through the visible‐light‐promoted reaction of the corresponding N‐alkoxyphthalimides with Hantzsch ester as the ...reductant. The alkoxy radicals subsequently undergo β‐scission of the C−C bond to generate carbon‐centered radicals, which are trapped by alkynyl‐, alkenyl‐, or allylsulfones.
Ring‐opening alkynylation, alkenylation, and allylation of cyclic hemiacetal derivatives under visible‐light irradiation conditions with Hantzsch ester (HE) as the reductant have been developed. Photoinduced generation of alkoxy radicals, β‐scission, and the trapping of the generated carbon‐centered radicals by alkynyl‐, alkenyl‐, or allylsulfones are involved in these transformations (see scheme).
The construction of all-carbon quaternary centers in small-ring systems is important but challenging in organic synthesis. Herein, by taking gem-difluorocyclopropyl bromides (DFCBs) as a type of ...general and versatile building block, we developed a practical method for building all-carbon quaternary centers in gem-difluorinated cyclopropanes (DFCs). The reaction relies on the involvement of a gem-difluorocyclopropyl radical intermediate, which can couple with a wide range of nucleophiles under copper catalysis.
Highlights • Overview of ABC transporters in the role of MDR. • Inhibitors of ABC transporters will be useful tools in the modulation of MDR. • Recent developments of RNA interference which involved ...in ABC transporter-mediated MDR. • Epigenetic regulators exhibit effective function on the ABC transporter-mediated MDR.
It has been a challenging topic and perpetual task to design and synthesize covalent macrocycles with characteristic self-assembling behaviors and excellent host-guest properties in supramolecular ...chemistry. Herein, we present a family of macrocyclic diphenylaminenarenes (DPAns, n = 3-7) consisting of methyldiphenylamine units through a facile one-pot synthesis strategy. Unlike many other reported macrocyclic arenes, the resultant non-planar DPAns feature intrinsic π-π stacking interactions, interesting self-assembling behaviors and ethene/ethyne capture properties. Specifically, strong multiple intermolecular edge-to-face aromatic interactions in DPA3 have been systematically investigated both in solid and solution states. The intriguing findings on the intermolecular edge-to-face stacking interaction mode in the macrocycle would further highlight the importance of noncovalent π-π interaction in supramolecular self-assembly. This study will also shed light on the macrocyclic and supramolecular chemistry and, we expect, will provide a direction for design and synthesis of covalent macrocycles in this area.
3,4‐Dihydroquinolinones were synthesized by the palladium‐catalyzed, oxidative‐addition‐initiated activation and arylation of inert C(sp3)H bonds. Pd(OAc)2 and P(o‐tol)3 were used as the catalyst ...and ligand, respectively, to improve the efficiency of the reaction. A further advantage of this reaction is that it could be performed in air. A relatively rare seven‐membered palladacycle was proposed as a key intermediate of the catalytic cycle.
3,4‐Dihydroquinolinones were synthesized by the palladium‐catalyzed, oxidative‐addition‐initiated activation and arylation of inert C(sp3)H bonds. Pd(OAc)2 and P(o‐tol)3 were used as the catalyst and ligand, respectively, to improve the efficiency of the reaction. A further advantage of this reaction is that it could be performed in air.
Herein, we report an effective method to offer chiral gem-difluorinated cyclopropanes containing an all-carbon quaternary stereocenter by rhodium-catalyzed stereoablative kinetic resolution. The ...activation of a sterically hindered all-carbon quaternary C–C bond through oxidative addition with a chiral rhodium complex is proposed as the enantiodetermining step. A wide range of gem-difluorinated cyclopropanes can be obtained with excellent ee values (ee = 87% to >99.9%), which are demonstrated to be useful chiral fluorine-containing building blocks by a series of postfunctionalizations.
Recent expansion of the scale of human activities poses severe threats to Earth’s life-support systems. Increasingly, protected areas (PAs) are expected to serve dual goals: protect biodiversity and ...secure ecosystem services. We report a nationwide assessment for China, quantifying the provision of threatened species habitat and four key regulating services—water retention, soil retention, sandstorm prevention, and carbon sequestration—in nature reserves (the primary category of PAs in China). We find that China’s nature reserves serve moderately well for mammals and birds, but not for other major taxa, nor for these key regulating ecosystem services. China’s nature reserves encompass 15.1% of the country’s land surface. They capture 17.9% and 16.4% of the entire habitat area for threatened mammals and birds, but only 13.1% for plants, 10.0% for amphibians, and 8.5% for reptiles. Nature reserves encompass only 10.2–12.5% of the source areas for the four key regulating services. They are concentrated in western China, whereas much threatened species’ habitat and regulating service source areas occur in eastern provinces. Our analysis illuminates a strategy for greatly strengthening PAs, through creating the first comprehensive national park system of China. This would encompass both nature reserves, in which human activities are highly restricted, and a new category of PAs for ecosystem services, in which human activities not impacting key services are permitted. This could close the gap in a politically feasible way. We also propose a new category of PAs globally, for sustaining the provision of ecosystems services and achieving sustainable development goals.
The efficient removal of alkyne impurities for the production of polymer-grade lower olefins remains an important and challenging goal for many industries. We report a strategy to control the pore ...interior of faujasite (FAU) zeolites by the confinement of isolated open nickel(II) sites in their six-membered rings. Under ambient conditions, Ni@FAU showed remarkable adsorption of alkynes and efficient separations of acetylene/ethylene, propyne/propylene, and butyne/1,3-butadiene mixtures, with unprecedented dynamic separation selectivities of 100, 92, and 83, respectively. In situ neutron diffraction and inelastic neutron scattering revealed that confined nickel(II) sites enabled chemoselective and reversible binding to acetylene through the formation of metastable Ni(II)(C
H
)
complexes. Control of the chemistry of pore interiors of easily scalable zeolites has unlocked their potential in challenging industrial separations.
Infrared spectroscopic study of neutral water clusters is crucial to understanding of the hydrogen-bonding networks in liquid water and ice. Here we report infrared spectra of size-selected neutral ...water clusters, (H₂O)n (n = 3–6), in the OH stretching vibration region, based on threshold photoionization using a tunable vacuum ultraviolet free-electron laser. Distinct OH stretch vibrational fundamentals observed in the 3,500–3,600-cm−1 region of (H₂O)₅ provide unique spectral signatures for the formation of a noncyclic pentamer, which coexists with the global-minimum cyclic structure previously identified in the gas phase. The main features of infrared spectra of the pentamer and hexamer, (H₂O)n (n = 5 and 6), span the entire OH stretching band of liquid water, suggesting that they start to exhibit the richness and diversity of hydrogenbonding networks in bulk water.
Comprehensive Summary
The chemistry of alkoxy radicals was extensively explored during the period of 1960s to 1990s, but it has remained dormant for the past few decades. Recently, alkoxy radicals ...attract the attentions again, because new methods for generating alkoxy radical species have emerged. These newly developed methods are mainly based on the photolysis by visible light under mild conditions, thus allowing for new transformations of the carbon‐centered radical species that are generated from the β‐scission or hydrogen ion of the alkoxy radicals. Herein, we demonstrate that the alkoxy radicals derived from cyclic hemiacetals can be generated through visible‐light‐induced electron transfer with sodium iodide and triphenylphosphine as the catalyst. The alkoxy radicals subsequently undergo β‐scission to generate carbon‐centered radicals, which are trapped by cinnamic acids, aryl alkenes, vinylboronic acid and silyl enol ether to deliver the corresponding C—C bond forming products. This catalytic method for ring‐opening alkenylation reaction of cyclic hemiacetal derivatives under visible‐light irradiation conditions demonstrates the compatibility of the visible light‐promoted alkoxy radical generation method with various carbon radical trapping processes. This work opens up new possibilities for the application of alkoxy radicals in organic synthesis.
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