Synthesis chelation

Reactions via carboxyheterocyclic magnesium chelates Synthesis with addition of 2 C-atoms u-Aminocarboxylic acids from halides via hydantoins... 

Silica is an alternative host for lanthanide chelates. Synthesis of nanosized silica particles by well-estabhshed hydrolysis of tetraethylorthosihcate (TEOS) with ammonium hydroxide is a common route for particle preparation. The transparent inert silica material is an excellent matrix for dye-embedded nanolabels as less spectral interferences are expected from the host material. Multiple lanthanide particles have been prepared for bioanalysis. Nanoparticles have been S3Uithesized by hydrolysis of TEOS with ammonium hydroxide in a microemulsion-containing aqueous solution of N,iV,iV, N -[2,6-bis(3 -aminomethyl-l -pyrazolyl)-phenylpyri-dine]tetrakis(acetate)-Tb(in) (BPTA-Tb ) chelate. In the microemulsion, the aqueous phase containing the lanthanide chelate formed nanodroplets acting as nanoreactors for the synthesis of nanoparticles. Since the size of the nanoparticles is dependent on the size of the droplets, it can be controlled, e.g., by the t3q>e of surfactants and by adjusting the concentration of the reactants [42-46],... 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Chelation itself is sometimes useful in directing the course of synthesis. This is called the template effect (37). The presence of a suitable metal ion facihtates the preparation of the crown ethers, porphyrins, and similar heteroatom macrocycHc compounds. Coordination of the heteroatoms about the metal orients the end groups of the reactants for ring closure. The product is the chelate from which the metal may be removed by a suitable method. In other catalytic effects, reactive centers may be brought into close proximity, charge or bond strain effects may be created, or electron transfers may be made possible. 

When the reaction of acetaldehyde with a 6-diazopenicillanate is catalyzed by BFs-EtiO, an epoxide of unknown stereochemistry is obtained (79H( 13)227). With ZnCh catalysis, however, the 6a-acetyl derivative is obtained, which can be stereospecifically reduced as the Mg chelate to the 6a-(/ -l-hydroxyethyl) derivative as part of an elegant synthesis of the carbapenem thienamycin (Scheme 40) (8UA6765). 

The first synthesis of enterobactin, a microbial chelator and transporter of environmental iron, was accomplished by the coupling of three protected L-serine units and macrocyclization by the double activation method. 

Complexes with chelating organic reagents such as salicylaldehyde and -diketonales were first prepared by N. V. Sidgwick and his students in 1925, and many more have since been characterized, Stability, as measured by equilibrium formation conslanis, is rather low and almost invariably decreases in the sequence Lj > Na > K. This situation changed drainalically in 1967 w hen C. J. Pedersen announced the synthesis of several macrocyclie polyethers which were shown to form stable complexes with... 

Several of the catena-Scx anions have proved to be effective chelating ligands to both main-group and transition metals. Synthesis of the... 

The Knorr pyrazole synthesis has been extensively utilized in the preparation of a number of pyrazoles as metal chelators, photographic dyes, herbicides, and biologically active... 

Synthesis, reactions, and metal-chelating properties of functionalized heterocycles possessing N-hydroxyamide moiety 97YGK524. 

Synthesis, structure, and transformations of a-pyrone derivatives, viz., xanthy-rones, glaucyrones, and chelated magnesium enolates 98T8243. 

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