Homogeneous gold-catalyzed cyclopropanation has emerged as a powerful method in organic synthesis due to its rich chemistry and fascinating reactivity. This thriving strategy is remarkable for its ...mild conditions, good selectivity, and high efficiency, which provides complementarity and orthogonality to traditional metal-catalyzed cyclopropanation. This review summarizes recent advances in gold-catalyzed cyclopropanation divided by the type of carbenoid precursors. Besides the commonly used
diazo compounds
, current approaches enable readily available
enynes
,
propargyl esters
,
cyclopropenes
,
cycloheptatrienes
,
alkynes, and sulfonium ylides
as safer surrogates in the realm of gold carbenoid chemistry. Meanwhile, these reactions allow for the rapid building of molecular complexity including synthetically useful and intricate cyclic, heterocyclic, and polycyclic skeletons. The combination of the new reactivity of gold complexes with their capability to catalyze cyclopropanations may lead to myriad opportunities for the design of new reactions. Furthermore, the synthetic utilities of such superior methods have also been illustrated by the total syntheses of selected natural and biologically interesting products and the asymmetric formation of challenging target molecules.
This review highlights recent advances in gold-catalyzed selective cyclopropanation divided by the type of carbenoid precursors.
During the past few decades, there has been considerable growth in the development of denitrogenative reactions of triazole skeletons to construct valuable cyclic compounds, particularly ...heterocycles. Despite the inherent difficulty of the ring‐opening of triazole derivatives, many novel and efficient approaches have arisen in this area mainly with the use of transition metal (such as rhodium, palladium, silver, copper) catalysis, photolysis, or free radical mediated reactions. Generally, these procedures begin with the ring‐opening of 1,2,3‐triazoles or benzotriazoles followed by N2 extrusion and subsequent diverse transformations, which enable the rapid synthesis of various heterocycles in a single step. To avoid overlap with other related reviews, this minireview covers the recent advances in the denitrogenative cyclization of 1,2,3‐triazoles since 2016 and the denitrogenative cyclization of benzotriazoles since 2012.
Open source: Denitrogenation is a very powerful ring‐opening strategy for triazole rings and attracts considerable attention from the organic synthetic community. The reactions of different types of triazoles and benzotriazoles as the precursors for generating carbene or diazonium species provide access to diverse synthetically valuable heterocycles. An overview of the denitrogenative cyclization reaction of triazoles and benzotriazoles is presented.
Over the past years, the metal‐catalyzed dearomative cycloaddition of 3‐nitroindoles and 2‐nitrobenzofurans have emerged as a powerful protocol to construct chiral fused heterocyclic rings. However, ...organocatalytic dearomative reaction of these two classes of heteroarenes has become a long‐standing challenging task. Herein, we report the first example of phosphine‐catalyzed asymmetric dearomative 3+2‐cycloadditio of 3‐nitroindoles and 2‐nitrobenzofurans, which provide a new, facile, and efficient protocol for the synthesis of chiral 2,3‐fused cyclopentannulated indolines and dihydrobenzofurans by reacting with allenoates and MBH carbonates, respectively through a dearomative 3+2‐cycloaddition.
The first example of phosphine‐catalyzed asymmetric dearomative 3+2‐cycloaddition of 3‐nitroindoles and 2‐nitrobenzofurans was realized, which provides a new, facile, and efficient protocol for the synthesis of chiral 2,3‐fused cyclopentannulated indolines and dihydrobenzofurans by reacting with allenoates and MBH carbonates, respectively.
Gold‐Catalyzed Enantioselective Annulations Li, Yangyan; Li, Wenbo; Zhang, Junliang
Chemistry : a European journal,
January 12, 2017, Letnik:
23, Številka:
3
Journal Article
Recenzirano
In the past decade, there have been many extraordinary advances in the development of gold‐catalyzed enantioselective annulations, such as cycloadditions, cyclizations, cycloisomerizations, and ...tandem annulations, which are of particular interest owing to their potential for rapid construction of optically active hetero‐ and carbocyclic molecules. This Review summarizes the methods to construct chiral cyclic compounds by gold‐catalyzed enantioselective annulations reported since 2005. The Review is organized according to the general annulation types catalyzed by chiral gold complexes or chiral gold salts, which have four main types (cycloadditions, cyclizations of C−C multiple bonds with tethered nucleophiles, cycloisomerization or cyclization of enynes, and tandem annulations), as well as some other strategies. The general reaction mechanisms of each subcategory, key intermediates for some unusual transformations, and the application of several novel ligands and chiral gold salts are also discussed.
Good as gold: Methods to construct chiral cyclic compounds by gold‐catalyzed enantioselective annulations reported since 2005 are summarized, including discussion of four main types of annulation (cycloadditions, cyclizations of C−C multiple bonds with tethered nucleophiles, cycloisomerization or cyclization of enynes, and tandem annulations).
With the conventional Haber-Bosch NH
3
synthesis in industry requiring harsh pressures and high temperatures, artificial N
2
fixation has been long sought after. The electrochemical nitrogen ...reduction reaction (NRR) could offer a solution by allowing NH
3
production under ambient conditions. In this review, important recent findings on theoretical calculations and experimental exploration on the NRR at room temperature are systematically reviewed. Firstly, we discuss the mechanism of electrochemical heterogeneous catalysis for the NRR. The NRR is a multi-proton coupled electron transfer (PCET) process which implies that in addition to catalyst surface size effects, ligand and strain effects will also significantly influence the binding energy of the adsorbed N atoms, reaction intermediates and product species. Electrocatalysts including metals, metal nitrides, metal oxides and carbon-based materials will also be discussed at length. A linear scaling relationship seems to limit the NRR activity on most metals and metal oxides. Metal nitrides, however, follow the Mars-van Krevelen (MvK) mechanism which usually shows a lower potential energy barrier compared to the associative mechanism. Carbon-based materials and some single atom catalysts exhibit improved activity and selectivity due to ligand effects. Thus, electrolytes containing a proton donor might play a crucial role in the NRR. The limiting concentration of proton donors and the rate of proton transport to the active sites might be effective factors in boosting the selectivity of the NRR. Specifically, ionic liquids with high N
2
solubility demonstrate much larger faradaic efficiency and would be promising candidates for use in NRR processes. Inspired by the characteristics of PCET, four strategies of electrode engineering were introduced including limiting protons, tuning the electron transport, modifying the electrode structure facilitating mass transport, and completely changing the NRR mechanism inspired by bio-nitrogenase and Li mediated N
2
fixation.
The fundamental basics, electrocatalysts, electrolytes, and electrode design for the nitrogen reduction reaction under ambient conditions were comprehensively reviewed.
Display omitted
•It is the first time to report visible light photodegradation of tetracycline (TC) over TiO2.•56.7% of TC was removed by TiO2 under visible (500 nm) light irradiation.•Different ...active species were found in TC degradation under different light irradiations.•UV and visible light irradiations generated different degradation products.
TiO2 is widely exploited as a photocatalyst to degrade antibiotic residues in water under UV irradiation, but it is inefficient for visible light photocatalysis due to its large band gap. Herein, it is the first time to report the photodegradation of tetracycline (TC) over TiO2 under visible light irradiation. 25.1% of removal efficiency for TC was achieved even under 700 nm light irradiation. Furthermore, it was demonstrated that O2− species, which were generated from photoexciting of a surface complex between TC molecules and TiO2, played a critical role in the visible light photocatalytic degradation of TC. In addition, it was found that the visible light photocatalytic degradation generated different active species and intermediate products from those under UV irradiation. N-doped TiO2 exhibited even better performance for visible-light photocatalytic degradation of TC with higher removal efficiency and larger mineralization rate, which followed different degradation-mechanism.
3D copper nanowires-thermally annealed graphene aerogel (CuNWs-TAGA) framework is firstly prepared by freeze-drying followed by thermal annealing from CuNWs, graphene oxide (GO) and L-ascorbic acid. ...Epoxy resin is then poured back into the above 3D CuNWs-TAGA framework to fabricate the CuNWs-TAGA/epoxy nanocomposites. CuNWs with average diameter of about 120 nm and length of approximate 10 μm are successfully prepared. When the mass fraction of CuNWs-TAGA is 7.2 wt% (6.0–1.2 wt% CuNWs-TAGA), the thermal conductivity coefficient (λ) value of the CuNWs-TAGA/epoxy nanocomposites reaches the maximum of 0.51 W/mK. Meantime, the CuNWs-TAGA/epoxy nanocomposites exhibit the maximum electromagnetic interference shielding effectiveness (EMI SE) value of 47 dB and electrical conductivity (σ) of 120.8 S/m, ascribed to perfect 3D CuNWs-TAGA conductive network structures. Meanwhile, the corresponding elasticitymodulus, hardness, glass transition temperature (Tg) and heat-resistance index (THRI) of the CuNWs-TAGA/epoxy nanocomposites increase to 4.69 GPa, 0.33 GPa, 126.3 °C and 181.7 °C, respectively.
P‐stereogenic tert‐ and sec‐phosphines have wide applications in asymmetric catalysis, materials, and pharmaceutical chemistry, however, their practical synthesis still constitutes a significant ...challenge. Herein, a successful kinetic resolution of rac‐secondary phosphine oxides via the enantioselective P‐benzylation process catalyzed by the palladium/Xiao‐Phos was designed. Both tert‐ and sec‐phosphine oxides were delivered in good yield and excellent enantiopurity (selectivity factor up to 226.1). The appealing synthetic utilities are further demonstrated by the facile preparation of several valuable P‐chiral compounds, precursors of bidentate ligands, as well as transition metal complexes.
A kinetic resolution of rac‐secondary phosphine oxides via the enantioselective P‐benzylation process catalyzed by the palladium/Xiao‐Phos was designed. Both, tert‐ and sec‐phosphine oxides were delivered in good yield and excellent enantiopurity (selectivity factor up to 226.1). The synthetic utilities are further demonstrated by the facile preparation of several P‐chiral compounds, precursors of bidentate ligands, and transition metal complexes.
The development of transition-metal-catalyzed methods for the synthesis of P-chiral phosphine derivatives poses a considerable challenge. Herein, we present a direct Pd/Xiao-Phos-catalyzed ...cross-coupling reaction of easily accessible secondary phosphine oxides and aryl bromides, which provides rapid access to P-chiral phosphine oxides. The reaction proceeds efficiently with a wide array of reaction partners to deliver various tertiary phosphine oxides in up to 96% yield and 97% ee. Moreover, the synthesis of DiPAMP ligand and its analogues was also realized, which demonstrates a suitable pathway to switching the branched chain of DiPAMP.
Proton exchange membrane water electrolysis (PEMWE), as a promising technology for hydrogen production from renewable energy sources, has great potential for industrial application. Gas bubbles are ...known to influence the PEMWE cell performance significantly, but a full picture of bubble behaviors and their impacts on cell performance has been lacking. In this review, we first discuss the most recent advances toward understanding the bubble evolution and transport processes as well as the mechanisms of how bubbles impact the PEMWE. Then the state-of-the-art bubble management methods to mitigate bubble-induced performance losses are summarized. Due to the similarity between PEMWE and anion exchange membrane water electrolysis (AEMWE), we also extend related discussions for AEMWE. Lastly, we present principles of bubble management, followed by an outlook of scientific questions and suggestions for future research priorities.
