Silver Catalysis Research Articles

Silver-Catalyzed Asymmetric Mannich Reaction of Isatin-Based Ketimines

Key words silver catalysis - Mannich reaction - asymmetric catalysis - isatin ketimines - diazomethylphosphonates

One-Pot Synthesis of 1-Substituted 1H-Isochromenes by Combining Brønsted Acid with Silver Catalysis

A one-pot synthesis of 1-substituted 1<i>H</i>-isochromenes employing various 2-alkynyl-benzaldehydes and ketones as substrates under a combination of Brønsted acid and silver catalysis has been developed. The isochromenes, which are present as important heterocyclic core structures in many bioactive and natural compounds, are obtained in medium to excellent yields with diastereomeric ratios of up to 9:1. A first enantioselective variant has also been tested.

ChemInform Abstract: Silver &amp; Gold‐Catalyzed Routes to Furans and Benzofurans

AbstractReview: [140 refs.

Dual cobalt(II)/silver catalysis: synthesis of aryliminated pyrrolo[2,3-b]indoles via multicomponent bicyclization cascades

Dual cobalt(II)/silver catalysis enables multicomponent bicyclization cascades of 2-ethynylanilines, tert-butyl isocyanide, and arylamines, resulting in subsequent multiple bond-forming events to rapidly build up aryliminated pyrrolo[2,3-b]indoles. The reaction pathway involves bimetal-catalyzed isocyanide insertion/1,3-dipolar cycloaddition/imination substitution sequence.

Silver-Catalyzed Isocyanide-Isocyanide [3+2] Cross-Cycloaddition Involving 1,2-Group Migration: Efficient Synthesis of Trisubstituted lmidazoles.

Imidazole ring is an important five-membered aromatic heterocycle that is widely present in natural products and synthetic molecules. The isocyanide-isocyanide [3+2] cross-cycloaddition reaction constitutes a straightforward method to access imidazoles starting from the easily available chemicals. So far, only three successive reports are known and all lead to the formation of 1,4-disubstituted imidazoles. Here, we report the first isocyanide-isocyanide [3+2] cross-cycloaddition reaction allowing for the formation of 1,4,5-trisubstituted imidazoles under silver catalysis. An unexpected 1,2-migration of sulfonyl, alkoxycaybonyl, and carbamoyl groups took place during the cyclization process that is responsible for the formation of trisubstituted imidazoles. This report displayed a mechanistically novel synthetic method toward a variety of imidazole derivatives, which are otherwise difficult to access by conventional methods.

Enhanced Oxygen and Hydroxide Transport in a Cathode Interface by Efficient Antibacterial Property of a Silver Nanoparticle-Modified, Activated Carbon Cathode in Microbial Fuel Cells.

A biofilm growing on an air cathode is responsible for the decreased performance of microbial fuel cells (MFCs). For the undesired biofilm to be minimized, silver nanoparticles were synthesized on activated carbon as the cathodic catalyst (Ag/AC) in MFCs. Ag/AC enhanced maximum power density by 14.6% compared to that of a bare activated carbon cathode (AC) due to the additional silver catalysis. After operating MFCs over five months, protein content on the Ag/AC cathode was only 38.3% of that on the AC cathode, which resulted in a higher oxygen concentration diffusing through the Ag/AC cathode. In addition, a lower pH increment (0.2 units) was obtained near the Ag/AC catalyst surface after biofouling compared to 0.8 units of the AC cathode, indicating that less biofilm on the Ag/AC cathode had a minor resistance on hydroxide transported from the catalyst layer interfaces to the bulk solution. Therefore, less decrements of the Ag/AC activity and MFC performance were obtained. This result indicated that accelerated transport of oxygen and hydroxide, benefitting from the antibacterial property of the cathode, could efficiently maintain higher cathode stability during long-term operation.

ChemInform Abstract: Silver‐Catalyzed 7‐exo‐dig Cyclization of Silylenolether‐ynesulfonamides.

AbstractCyclization of silylenolether‐ynesulfonamides proceeds at ambient temperature under mild reaction conditions under silver catalysis.

Synthesis of Chiral Spiro-nitroprolinates by Silver(I) Catalysis

Key words silver catalysis - phosphine ligands - nitroprolinates - 1,3-dipolar cycloaddition

ChemInform Abstract: Enantioselective Synthesis of 4H‐Pyranonaphthoquinones via Sequential Squaramide and Silver Catalysis.

AbstractThe title synthesis is achieved from naphthoquinones [e.g. (I)] and alkyne‐tethered nitroalkenes [e.g. (II)] via a one‐pot sequential Michael addition/hydroalkoxylation reaction which are catalyzed by squaramide and silver(I) salt, respectively.

ChemInform Abstract: Asymmetric Synthesis of Spiropyrazolones by Sequential Organo‐ and Silver Catalysis.

AbstractAn asymmetric Michael addition and a formal Conia‐ene reaction give rise to a stereoselective one‐pot synthesis of spiropyrazolones.

ChemInform Abstract: Silver‐ versus Gold‐Catalyzed Sequential Oxidative Cyclization of Unprotected 2‐Alkynylanilines with Oxone.

Unprecedented domino oxidative cyclization reactions of unprotected 2-alkynylanilines to give functionalized 4H-benzo[d][1,3]oxazin-4-one or benzisoxazole derivatives in moderate to good yields are achieved by silver vs. gold selective catalysis. The search for the optimal reaction conditions revealed the divergent catalytic activity of NaAuCl4·H2O and AgNO3.

Silver‐Catalyzed 7‐exo‐dig Cyclization of Silylenolether‐ynesulfonamides

AbstractCyclization of silylenolether‐ynesulfonamides proceeds at ambient temperature under mild reaction conditions under silver catalysis. Bridged compounds were obtained exclusively through 7‐exo‐dig reactions. The protocol is applicable to a wide range of substrates, thus leading to azabicyclic frameworks.

Silver-Catalyzed 7-exo-dig Cyclization of Silylenolether-ynesulfonamides.

Cyclization of silylenolether-ynesulfonamides proceeds at ambient temperature under mild reaction conditions under silver catalysis. Bridged compounds were obtained exclusively through 7-exo-dig reactions. The protocol is applicable to a wide range of substrates, thus leading to azabicyclic frameworks.

ChemInform Abstract: Copper Catalysis for Synthesizing Main‐Group Organometallics Containing B, Sn or Si

AbstractReview: [51 refs.

Graphene Based Functional Hybrid Nanostructures: Preparation, Properties and Applications

The intent of this chapter is to provide a basic overview of recent advances in graphene based hybrid nanostructures including their preparation, properties and potential applications in various field. The development of graphene based functional materials, has shown their tremendous interest in areas of science, engineering and technology. These materials include graphene supported inorganic nanomaterials and films, graphene-metal decorated nanostructures, Core/shell structures of nanocarbon-graphene and graphene doped polymer hybrid nanocomposites etc. They have been prepared by various methods like chemical vapor deposition of hydrocarbon on metal surface, liquid phase exfoliation of graphite, chemical reduction of GO, silver mirror reaction, catalysis, in-situ hydroxylation and sono sol-gel route, respectively. The attractive properties of graphene and their derivatives filled with metal nanoparticles (e.g. Au, Ag, Pd, Pt, Ni, and Cu) have made them ideal templates. Graphene and their derivatives have also been decorated with various semiconductor nanomaterials (e.g. metal oxides and dioxides, metal sulfides). These metal decorated graphene nanostructures can be useful as functional hybrid nanomaterials in electronics, optics, and energy based products like solar cells, fuel cells, Li-ion batteries and supercapacitors, ion exchange and molecular adsorption.

Copper Catalysis for Synthesizing Main-Group Organometallics Containing B, Sn or Si.

A copper complex has proven to be a potent catalyst for forming a C–B bond via diborylation of arynes and alkynes, affording vic‐diborylarenes and vic‐diborylalkenes with high efficiency. A boryl‐substituted organocopper species, which is intermediately generated in the diborylation, has been found to be captured by a tin or a carbon electrophile, leading to three‐component borylstannylation or carboboration, in which C–B and C–Sn (or C) bonds are constructed simultaneously. Furthermore, reducing the Lewis acidity of the boron center with 1,8‐diaminonaphthalene decisively alters the regiochemical behavior of the borylcopper species, enabling the installation of a boryl moiety to occur at an internal carbon of terminal alkynes in borylstannylation and protoboration. Copper catalysis for C–Sn and C–Si bond‐forming processes via distannylation, hydrostannylation and silylstannylation, as well as silver catalysis for a C–B bond‐forming reaction, is also described.

Enantioselective synthesis of 4H-pyranonaphthoquinones via sequential squaramide and silver catalysis.

An enantioselective one-pot Michael addition/hydroalkoxylation reaction between 2-hydroxy-1,4-naphthoquinones and alkyne-tethered nitroalkenes catalyzed by a cinchona-derived squaramide and a silver(I) salt has been developed. The sequential protocol provides a direct access to 4H-pyranonaphthoquinones in moderate to very good yields and good to excellent enantioselectivities at a very low catalyst loading (0.5 mol%) of the squaramide.

Asymmetric Synthesis of Spiropyrazolones by Sequential Organo‐ and Silver Catalysis

AbstractA stereoselective one‐pot synthesis of spiropyrazolones through an organocatalytic asymmetric Michael addition and a formal Conia‐ene reaction has been developed. Depending on the nitroalkene, the 5‐exo‐dig‐cyclization could be achieved by silver‐catalyzed alkyne activation or by oxidation of the intermediate enolate. The mechanistic pathways have been investigated using computational chemistry and mechanistic experiments.

Asymmetric Synthesis of Spiropyrazolones by Sequential Organo- and Silver Catalysis.

A stereoselective one-pot synthesis of spiropyrazolones through an organocatalytic asymmetric Michael addition and a formal Conia-ene reaction has been developed. Depending on the nitroalkene, the 5-exo-dig-cyclization could be achieved by silver-catalyzed alkyne activation or by oxidation of the intermediate enolate. The mechanistic pathways have been investigated using computational chemistry and mechanistic experiments.

Gold- or Silver-Catalyzed Syntheses of Pyrones and Pyridine Derivatives: Mechanistic and Synthetic Aspects.

3-Oxo-5-alkynoic acid esters, on treatment with a carbophilic catalyst, undergo 6-endo-dig cyclization reactions to furnish either 2-pyrones or 4-pyrones in high yields. The regiochemical course can be dialed in by the proper choice of the alcohol part of the ester and the π-acid. This transformation is compatible with a variety of acid-sensitive groups as witnessed by a number of exigent applications to the total synthesis of natural products, including pseudopyronine A, hispidine, phellinin A, the radininol family, neurymenolide, violapyrone, wailupemycin and an unnamed brominated 4-pyrone of marine origin. Although the reaction proceeds well in neutral medium, the rate is largely increased when HOAc is used as solvent or co-solvent, which is thought to favor the protodeauration of the reactive alkenyl-gold intermediates as the likely rate-determining step of the catalytic cycle. Such intermediates are prone to undergo diauration as an off-cycle event that sequesters the catalyst; this notion is consistent with literature data and supported by the isolation of the gem-diaurated complexes 12 and 15. Furthermore, silver catalysis allowed access to be gained to 2-alkoxypyridine and 2-alkoxyisoquinoline derivatives starting from readily available imidate precursors.