Silver Reagents

After preliminary evaluation of the discovery route (scheme 1), we concluded that the overall yield of RWJ-26240 should be improved and that the use of NaCNBH. should be eliminated, since it produces a waste stream containing HCN or NaCN. Replacement of the expensive silver reagent, silver acetate, would permit significant cost reduction. The copper-catalyzed palladium coupling step would lead to palladium as a contaminant in the final product.177 Since a drug substance containing palladium would not be acceptable, this step would also have to be revised. 

Glycals can be transformed into 1,6-anhydro sugar derivatives by intramolecular cyclization in the presence of Lewis and Brpnsted acids, a reaction that has been termed the intramolecular Ferrier glycosylation.168 Sharma el al.169 showed that a montmorillonite clay-supported silver reagent can be an efficient catalyst for this transformation. The 1,6-anhydro-2,3-dehydro sugars obtained were then selectively dihydroxylated to furnish 1,6-anhydro saccharides. 

Several reaction conditions concerning the nature of the silver reagent were tested. Usually, anhydrous AgC104 was used as the initiator for the catalytic reaction, but AgAsF6 was found to work equally well. When the monohydrate AgC104 H20 was used... 

Note The reactions must be carried out by avoiding light exposure, because of the light-sensitive nature of the silver reagents. This is achieved by simply wrapping the glassware in aluminum foil.)... 

The homologation of carboxylic acids is a reaction frequently needed in synthetic chemistry. The Arndt-Eistert reaction though aesthetically pleasing, is not preferred today, owing to the use of diazomethane and silver reagents. We provided47 a solution to this problem by the addition of carbon radicals to... 

In this chapter, we concentrate on the applications of silver catalysts in preparative organic chemistry over the last decade (1994-2004). The use of stoichiometric amounts of silver reagents lies beyond the scope of this chapter. 

The binuclear lanthanide-silver reagent is formed by combining silver diketonate such as Ag(fod) with a lanthanide tris diketonate like Yb(fod)3 to give Ag+[Yb(fod)3]-. 

The spectra of 69a and 69b exhibited only small nonequivalence in the presence of Yb(hfc)3, whereas addition of Ag(fod) caused larger nonequivalence of methyl and methoxy resonances of the R-groups at 500 MHz . The binuclear dipyrromethene complex with Zn(n) (70) has a helical structure that renders it chiral. This was confirmed by a doubling of certain resonances in the H NMR spectrum of the zinc complex in the presence of Eu(tfc)3/Ag(fod) or Yb(tfc)3/Ag(fod). Splitting of the resonances was not observed in the presence of the lanthanide chelate alone and was only observed on addition of the silver reagent . 

Indirect methods using atomic absorption measuring techniques have also been worked out. These seldom-used procedures precipitate the chloride with silver reagent and detect the silver ions in the dissolved precipitate or the excess of them in the filtered reaction media [40,41]. A little more complicated versions of phenyl mercury(II) chloride complex, separates it by extraction with chloroform and detects the mercury by AAS. This allows one to analyze very dilute (0.015 ppm) chloride samples [42]. 

B. Positive spots are produced by an alkaline silver reagent (0.13/ silver nitrate, M ammonia, IM sodium hydroxide), but the chromatograms have to be treated with sodium thiosulfate and rinsed well with water... 

The solid curve in Fig. 3 shows the experimentally determined separatrix. Perturbations from the low iodide steady state were carried out using iodide and neutral iodide/iodate reagent. Perturbations from the high iodide steady state were carried out with silver reagent rapidly followed with iodate reagent. The unstable steady state determined by one-dimensional perturbations (open circle) compares well with the determination carried out by two-dimensional perturbations, indicated by the arrows on the composition line. 

The silver-promoted/catalyzed treatment of arylstannanes with electrophilic fluorine was effective method for the synthesis of aryl fluorides [82, 83]. Some of the early reports used an excess of the silver reagents to promote the reactions (Scheme 7.48). F-TEDA-PFg was an effective F+ source for these reactions, and the conditions were remarkably mild. One of the most attractive aspects of this chemistry was the speed of the reactions. 

A silver reagent with A7,iV -bis(mesitylmethyl)-1,2-diphenyl-1,2-ethanediamine 98 is useful reagent for determining the enantiomeric purity of alkenes. The reagent is prepared in the NMR tube by adding silver triflate, the amine ligand, and the substrate. 

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