Macrocycles pyridine

For example, concave pyridine macrocycle 166 [32] exhibited a chemoselectivity for O-protonation of nitronate anion in a buffered medium. 

Cupric acetate pyridine Macrocyclic polyacetylenes Oxidative coupling of acetylene derivatives s. lA, 770 (CHsCOO)2Cu CsHsN... 

Cupric acetate/pyridine Macrocyclic polyacetylenes (CHfiOO) CulCsH N 0... 

Whereas the unsubstituted parent compounds prepared by Jenny et al. (Section 2.2.1) were not considered likely to be able to act as ligands or hosts, some indications of the capacity of a//-homocalixarenes and -calixpyridines to bind to guests are given by the results of X-ray structure analyses. The cluster type inclusion of water by the pentameric pyridine macrocycle 38 via hydrogen bonds seems... 

Other indications of the template effect have been offered as well. Fenton, Cook and Nowell reported that the condensation of pyridine-2,6-dicarbaldehyde with 1,11-diamino-3,6,9-trioxaundecane in 1 1 molar ratio in butanol leads only to resinous gums . In the presence of equimolar amounts of Pb(SCN)2, the macrocycle illustrated in Eq. (2.5) was obtained in good yield . 

Newkome and his group have pioneered in the synthesis of aliphatic macrocycles containing the pyridine subcyclic unit " . Like the furan systems discussed in Sect. 3.6, these are macrocycles containing a potentially coordinating subcyclic unit whose donor... 

Similar compounds to those described above have been prepared by the same group using the bis-cesium salts of pyridine-3,5-dicarboxylic acids. In a number of experiments Piepers and Kellogg showed that Cs plays an irreplacable role as compared with Na", K and Rb for the formation of [the macrocycle shown below] . 

It should be stressed that there has been considerable interest in macrocycles containing the pyridine subcyclic unit, especially by Newkome and coworkers (see also Chap. 4). Most of his interest appears to have been focussed on polyethers rather than ester compounds. Bradshaw has also reported syntheses of compounds containing the pyridine subcyclic unit. ... 

We do not discuss in detail the cases of tautomerism of heterocycles embedded in supramolecular structures, such as crown ethers, cryptands, and heterophanes, because such tautomerism is similar in most aspects to that displayed by the analogous monocyclic heterocycles. We concentrate here on modifications that can be induced by the macrocyclic cavity. Tire so-called proton-ionizable crown ethers have been discussed in several comprehensive reviews by Bradshaw et al. [90H665 96CSC(1)35 97ACR338, 97JIP221J. Tire compounds considered include tautomerizable compounds such as 4(5)-substituted imidazoles 1///4//-1,2,4-triazoles 3-hydroxy-pyridines and 4-pyridones. 

Enantiomeric recognition of amino compounds by chiral macrocyclic receptors including pyridine or triazole subunits 97CRV3313. 

Pyridine-2-carboxylic acid is a structure element of the macrocycle 1,6-bis-deacetylevonine (Euonymus europaeus) (02CPB199). 

Picolinate and pyridine-2,6-carboxylate give stable complexes, with 4- and 6-coordination. Macrocycles like porphyrins afford silver(II) derivatives most remarkable is the reaction of the macrocycle meso-Me6[14]ane (Figure 4.13). 

Fig. 3. Dimeric and tetrameric macrocyclic structures obtained from (diethylboryl)pyridines...

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