Visible-light-driven thio-carboxylation of alkynes with CO_(2):facile synthesis of thiochromones

Difunctionalizing carboxylation of alkynes with CO_(2)is a sustainable and important strategy to generate valuable acrylate derivatives from both readily available starting materials.Such protocols,however,always suffer from the use of excess metallic reagents and transition metal residue.Herein,we report the first thio-carboxylation of alkynes with thiophenols and CO_(2),which is a visible-light-driven and transition metal-free process.In contrast to previous carboxylations of alkynes via two-electron activation of CO_(2),mechanistic and computational investigations suggest that the single-electron activation of CO_(2)is involved in the thio-carboxylation,rendering uniqueβ-carboxylation.The following cyclizing acylation affords important thiochromones efficiently.Moreover,the one-pot method features mild reaction conditions(room temperature,1 atmosphere of CO_(2)),high chemo-and regio-selectivity,easy scalability and facile derivatization of products to bioactive compounds.

Oxidative cyclopalladation triggers the hydroalkylation of alkynes

This report describes the oxidative cyclopalladation activation of a C≡C bond during the Pd-catalyzed hydroalkylation of alkynes and analyzes potential reaction pathways based on density functional theory calculations. The more favorable pathway in-volves an oxidative cyclopalladation to generate a palladacyclopropene intermediate, which is rarely examined in Pd-catalyzed alkyne transformations. The reaction pathway proposed herein is kinetically favorable relative to the commonly proposed alkyne insertion mode. Furthermore, the Laplacians of the electron density, interaction region indicators, Mayer bond orders, and localized orbital bonding are evaluated to determine the reaction processes and characterize the key intermediates. Theoretical calculations indicate covalent bonding between a Pd(II) center and the two C-atoms in three-membered palladacycle species. Finally, electrostatic potential analysis reveals that the regioselectivity is governed by the charge distribution on the palladacycle moiety during the protonation step.

Insights into pH-dependent transformation of gibberellic acid in aqueous solution:Transformation pathway,mechanism and toxicity estimation

Gibberellic acid(GA_(3))is widely used in agriculture and maybe transfer with groundwater flow,which is an endocrine disruptor,but few studies have focused on the transformation pathway and toxicity assessment of GA_(3)and its products.Here,GA_(3)and its transformation products in aqueous solution were identified and quantified by liquid chromatography mass spectrometry hybrid ion trap time-of-flight(LCMS-IT-TOF)and high-performance liquid chromatography(HPLC),respectively.The results showed that the half-life of GA_(3)transformation in ultrapure water was 16.1–24.6 days at p H=2.0–8.0,with the lowest half-life occurring at p H=8.0 and highest half-life occurring at p H=3.3.Isomerized gibberellic acid(Iso-GA_(3))and gibberellenic acid(GEA)were the main transformation products with a little hydroxy gibberellic acid(OH-GA_(3)).In North China groundwater,the mass balance of GA_(3)and its products was 76.2%,including Iso-GA_(3)(58%),GEA(7.9%),GA_(3)(7.3%)and OH-GA_(3)(3%)after reaching transformation equilibrium.Using Gaussian 09 for chemical computation,it was found that the transformation mechanism of GA_(3)was dependent upon the bond energy and the stereochemical feature of its molecular structure.GA_(3)always isomerized from theγ-lactone ring due to the lowest bond energy between the oxygen terminus of theγ-lactone ring and A ring.While GA_(3)and its transformation products all had developmental toxicity,the predicated LC 50(96 hr)and LD 50 of the main products of GA_(3)were much lower than those of GA_(3),indicating GA_(3)would be transformed into higher toxicity derivatives in water environments,posing a significant health risk to humans and the environment.

Visible-Light-Driven Anti-Markovnikov Hydrocarboxylation of Acrylates and Styrenes with CO_(2)

Light-driven carbon dioxide(CO_(2))capture and utilization is one of the most fundamental reactions in Nature.Herein,we report the first visible-light-driven photocatalyst-free hydrocarboxylation of alkenes with CO_(2).Diverse acrylates and styrenes,including challenging tri-and tetrasubstituted ones,undergo anti-Markovnikov hydrocarboxylation with high selectivities to generate valuable succinic acid derivatives and 3-arylpropionic acids.In addition to the use of stoichiometric aryl thiols,the thiol catalysis is also developed,representing the first visible-lightdriven organocatalytic hydrocarboxylation of alkenes with CO_(2).The UV-vis measurements,NMR analyses,and computational investigations support the formation of a novel charge-transfer complex(CTC)between thiolate and acrylate/styrene.Further mechanistic studies and density functional theory(DFT)calculations indicate that both alkene and CO_(2)radical anions might be generated,illustrating the unusual selectivities and providing a novel strategy for CO_(2)utilization.

Is the metal involved or not? A computational study of Cu(I)-catalyzed [4+1] annulation of vinyl indole and carbene precursor

The Cu(I)-catalyzed [4 + 1] annulation of vinyl indoles and a carbene precursor is a powerful method for constructing cyclopentaindole derivatives. Density functional theory(DFT) calculations were used to elucidate the mechanism and regioselectivity of this reaction. After Cu-assisted indole C3-alkylation, direct1,5-annulation was favored over the Cu-assisted annulation pathway. Furthermore, the regioselectivity for1,5-annulation was attributed to the generated five-membered-ring product being more stable than the three-membered-ring product from 1,3-annulation, which was the kinetically favored pathway.

Carbon dots-confined CoP-CoO nanoheterostructure with strong interfacial synergy triggered the robust hydrogen evolution from ammonia borane

Ammonia borane(NH_(3)BH_(3),AB) is promising for chemical hydrogen sto rage;however,current systems for rapid hydrogen production are limited by the expensive noble metal catalysts required for AB hydrolysis.Here we report the design and synthesis of a highly efficient and robust non-noble-metal catalyst for the hydrolysis of AB at 298 K(TOF=89.56 molH_(2) min^(-1) molCo^(-1)).Experiments and density functional theory calculations were performed to explore the catalyst’s hybrid nanoparticle heterostructure and its catalytic mechanism.The catalyst comprised nitrogen-doped carbon dots confining CoO and CoP,and exhibited strong interface-induced synergistic catalysis for AB hydrolysis that effectively decreased the energy barriers for the dissociation of both AB and water molecules.The co-doping of N and P introduced numerous defects,and further regulated the reactivity of the carbon layers.The heterogeneous interface design technique presented here provides a new strategy for developing efficient and inexpensive non-noblemetal catalysts that may be applicable in other fields related to energy catalysis.

Carbene-enabled ether activation through the formation of oxonium: a theoretical view

Here,we report a theoretical investigation of the reactivity and chemoselectivity of carbene-enabled ether activation.The mechanism obtained from DFT calculations revealed that the final products were dependent on the stability of the oxonium intermediate,which was afforded by nucleophilic attack of the corresponding ether onto a carbene species.Interestingly,we found that the nucleophilicity of ethers was crucial but not their solvation.Energy decomposition analysis based on absolutely localized molecular orbitals showed that the nucleophilicity of ethers was critical for polarization and charge transfer,leading to the chemoselectivity.

A facile and controllable one-pot synthesis approach to amino-functionalized hollow silica nanoparticles with accessible ordered mesoporous shells

The development of a practical synthetic method to functionalize hollow mesoporous silica with organic groups is of current intere st for selective adsorption and ene rgy storage applications.Herein,a facile and controllable one-pot approach for the synthesis of monodisperse amino-functionalized hollow mesoporous silica nanoparticles is presented.A novel solid-to-hollow structural transformation procedure of the silica nanoparticles is presented.The structural transformation is easily designed,as obse rved through transmission electro n microscopy,by tailo ring the HCl and N-lauroylsarcosine sodium molar ratio and the water content in the sol-gel.Ordered and radially oriented in situ aminofunctionalized mesochannels were successfully introduced into the shells of the hollow silica nanoparticles.A formation mechanism for the hollow mesoporous silica materials is discussed.

Efficient silver nanocluster photocatalyst for simultaneous methyl orange/4-chlorophenol oxidation and Cr(Ⅵ) reduction

Metal nanoclusters have shown great potential in photocatalysis,while simultaneous removal of both inorganic and organic contaminants by metal nanoclusters under visible light is less explored.Here,we synthesized Agm(SR)n(SR represents 3-mercaptopropyltriethoxysilane ligand) nanoclusters(~1 nm) via a reduction of silver triphenylphosphine under ambient conditions in the presence of 3-mercaptopropyltriethoxysilane.The nanocluster was characterized by UV-vis spectroscopy,high resolution transmission electron microscopy(HRTEM),Fourier transform infrared spectrum(FTIR),and X-ray photoelectron spectroscopy(XPS).Under 5 W blue LED,the Agm(SR)n/P25 exhibits enhanced catalytic activity for simultaneous methyl orange(MO) oxidation and Cr(Ⅵ) reduction,and also for synchronous 4-chlorophenol oxidation and Cr(Ⅵ) reduction.Mechanism studies by electrochemical impedance spectroscopy(EIS),photoluminescence(PL),electron spin resonance(ESR) etc.and control experiments reveal that the unique structure of silver nanoclusters with thiolate ligands is vital to the high catalytic performance,and both the photo-generated holes and superoxide radicals are responsible for the decomposition of MO.

A new fluorescent quinoline derivative toward the acid-responsivity in both solution and solid states

In this article,an acid-responsive luminescent material,1,4-di(quinoline-6-yl)buta-1,3-diyne(DQBD)is designed and synthesized.Upon different pH values,gradual changes of fluorescence colors for DQBD in both solution and solid phases are demonstrated due to the protonation effect.Moreover,such responsive characteristics can also be reversible,suggesting DQBD as a promising fluorescent material with great potential for reusable-and accurate-p H sensors in the future.