Crown ethers synthesis

Fig. 3a,b. Template cyclization reactions of a crown ethers and b CPOs. The coordination bonds are illustrated by black arrows. In the crown ether synthesis, ethylene glycols coordinate toward the metal acting as the template (normal template reaction) however, the template coordinates to the incorporated metals of porphyrin In CPO synthesis (inverse-template reaction)... 

Golubski, Z.E., Alkylation of phosphinic acid salts in the presence of crown ethers, Synthesis, 632, 1980. 

Among the 1,4-di-O-substituted-L-threitol derivatives (Figure 14a) the one that has found most use in chiral crown ether synthesis is the 1,4-dibenzyl ether. Not only has it provided (88, 106, 107) a ready entry into the chiral tetrasub-stituted 18-crown-6 derivatives ll-31 to ll-34, but it has also proved to be a usehil chiral precursor for the preparation of chiral disubstituted 9-crown-3 (107), 12-crown-4 (108), 15-crown-5 (108), and 18-crown-6 (109) derivatives l-57, l-58, l-59, and l-60, respectively. In the preparation of l-S8 the base-promoted cyclization with triethylene glycol ditosylate is best carried out (108) with a... 

Cesium fluoride, 21 234, 235, 237, 247 Cesium hexahalogenopolonite, 4 218 Cesium hydrogen phosphate, 4 14 Cesium ion, in crown ether synthesis, 21 24 Cesium isotope, halWife determination, 2 325-326... 

Arndt, S., Zeimentz, P.M., Spaniol, T.P. etal. (2003) Neutral and cationic trimethylsilylmethyl complexes of the rare earth metals supported by a crown ether synthesis and structural characterization. Dalton Transactions, 3622. 

There has been growing interest in the synthetic macrocyclic molecular rjeceptors since Pedersen s pioneering work on crown ether synthesis Separate reports, dealing... 

Alumina supported KF has been introduced by Ando etal.[42] and Clark etal.[43] as a basic catalyst for many types of the reactions such as o-methylation of phenol, crown ether synthesis, Michael addition of various nitroalkanes to unsaturated carbonyl compounds etc. 

The first proposal that a template effect is operative in such cases has been made by Greene, although a perusal of Pederson s original paper suggests that its seminal crown ether synthesis also relies on this effect. Cf. (a) C. J. Pedersen, J. Am. Chem. Soc. 1967,89, 7017-7036 (b) R. N. Greene, Tetrahedron Lett. 1972, 1793-1796. For a comprehensive treatise of the template effect in crown ether syntheses see [4] and literature cited therein. 

Cheneveit. R. Rodrigue, A. Beauchesne. P. Savoie. R. New complexes of the hydronium ion with crown ethers Synthesis and vibrational spectra. Can. J. Chem. 1984. 62. 2293-2298. 

Polycarboxylate Crown Ethers Synthesis, Complexation, Applications... 

This observation led to the notion that particular alkali metal cations appear to have specific affinities for different crown ethers. Greene s insight was to use the appropriate metal cation to template the formation of the crown in much the same way as transition metals had been used as templates for other, nitrogen containing, ligands and to experiment with different solvents. In every example of crown ether synthesis reported by Pedersen, the only metal cation present was Na" " (except in one case where K+ was used) as no hnk had been made between the size of the metal cation used and the target crown at that time. The purpose of a template in the synthesis of 18-crown-6 can be seen in Figure 3. The relationship between metal... 

Hetero-Crown Ethers—Synthesis and Metal-Binding Properties of Macrocyclic Ligands Bearing Group 16 (S, Se, Te) Donor Atoms... 

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