Water-soluble calix arenes

Water-soluble calix[ ]arenes (62 n = 4, 6, and 8) containing trimethylammonio-methyl groups act as efficient inverse phase-transfer catalysts in the nucleophilic substitution reactions of alkyl and arylalkyl halides with nucleophiles in water.126 (Inverse phase-transfer catalysts facilitate reactions between two immiscible reactants via the transport of an organic substrate into an aqueous solution of a second substrate, in which reactions take place.)... 

Baur. M. Frank. M. Schatz, J. Schildbach. F. Water-soluble calix[ ]arenes as receptor molecules for non-polar... 

Calix[n]arenes 1-3 were used as inverse PT catalysts in the alkylation of active methylene compounds with alkyl halides in aqueous NaOH solutions,and in aldol-type eondensation and Michael addition reactions. In the aikylation of phenylacetone with octyl bromide, the IPTC procedure enhanced the alkylation versus hydrolysis and C versus O alkylation selectivities with respect to those observed xmder classical PTC reactions in the presence of tetrabutylammonium bromide (TBAB) or hexadecyltributylammonium bromide (HTPB). Moreover, the aqueous catalyst solution was easily separated from the organic phase eontaining the products, and no organic solvent was required. In the case of the aldol-type condensation of benzaldehyde with indene or acetophenone in aqueous NaOH (Fig. 9), IPTC reaetions eatalyzed by I were compared with those conducted in aqueous micelles in the presence of cetyltrimethylammonium bromide (CTAB) as the sufactant. Although selectivities and yields were similar, the IPTC proeedure avoided the formation of emulsions, thus faciUtating product separation and catalyst recovery. In the light of the results obtained, water-soluble calix[ ]arenes 1-3 were proposed... 

Alkylation reactions of ketones, active methylene compoimds, alcohols, and phenols with alkyl halides occurred in quite good yields in aqueous NaOH solution without added organic solvent in the presence of water-soluble calix[ ]arene (n = 4,6, or 8) containing trimethy-lammoniomethyl groups acting as a reverse phase-transfer catalyst (Scheme 8.20). ° ... 

Alternatively, the Sn2 nucleophilic substitution reaction between alcohols (phenols) and organic halides under basic conditions is the classical Williamson ether synthesis. Recently, it was found that water-soluble calix[n]arenes (n = 4, 6, 8) containing trimethylammonium groups on the upper rim (e.g., calix[4]arene 5.2) were inverse phase-transfer catalysts for alkylation of alcohols and phenols with alkyl halides in aqueous NaOH solution to give the corresponding alkylated products in good-to-high yields.56... 

A new water-soluble calix[4]arene-triacid-monoquinone (99) has been synthesized and its ion-binding properties in aqueous solution were investigated by means of voltammetry and UV-visible spectrophotometry. The electrochemical behaviour of (99) is dependent on the concentration of Ca + ion rather than that of other alkaline... 

Arena, G., Contino, A., Gulino, F. G., Magri, A., Sansone, F., Sciotto, D., and Ungaro, R. (1999) Complexation of native I a-aminoacids by water soluble calix[4]arenes, Tetrahedron Lett. 40, 1597-1600. 

Calixarene esters are easily available by alkylation with ethyl bromoacetate and are often used as starting materials for the introduction of chiral groups at the narrow rim. Their aminolysis by chiral amines led to chiral calixarene derivatives in high yields. Water soluble calix[4]arene amino acid derivatives 9a,b obtained in this way, were successfully used as a pseudostationary phase... 

Novel water-soluble calix[4]arenes with phosphane-containing groups were synthesized by Shimizu et al. The beneficial effect of water-soluble phospha-... 

A systematic study to design neutral, water-soluble calix[4]arenes has been carried out by Gansey et al., and this has led to the synthesis of calixarene derivatives with water solubility up to 0.3 M [80]. 

Figure 59 A water-soluble calix[6]arene host and ferrocene-derived guests [82]...

The study of the interaction between calix[n]arene derivatives and biomolecular cationic functions is mainly limited to two groups of anionic water-soluble calix[n]ar-rene derivatives, the para-sulfonato- and 1,3-diphosphate systems. These anionic molecules complex strongly to the cationic lateral chains of the amino acids, lysine (Lys, K). arginine (Arg, R). and histidine (His. M). Association constants, as determined by NMR and microcalorimetry, for these three amino acids vary as follows His [Pg.141]

Fig. 8 Water-soluble calix[n]arenes and their monomeric units. Adapted from Ref. [48].

Fig. 9 Condensation of benzaldehyde with indene or acetophenone catalyzed by the water-soluble calix[4]arene 1. Adapted from Ref. [50].

Shimizu. S. Shirakawa, S. Sasaki, Y. Hirai. C. Novel water-soluble calix[4]arene ligands with phosphane-con-taining groups for dual functional metal-complex catalysts ... 

R = n-QHi3 Figure 2.64 Water-soluble calix[6] arenes (146). 

Water-soluble calix[n]arenes (n = 4, 6, and 8) with ammonium groups were used as high-performance inverse phase-transfer catalysts in the nucleophilic substitution reaction in water, (Scheme 4.6) [52]. The efficiency of the calix[n] arenes as catalysts varied with the size and/or shape of the substrate molecules. 

Calixarenes similarly to natural detergents easily embed the micelles and bilayers formed by other amphiphiles [54] and can exhibit highly selective catalytic activity as enzyme-mimicking systems. Thus, water-soluble calix[6]arenes 8-11 catalyzed the hydration of 1,4-dihydronicotinamide derivatives, important model compound used to study the properties of the reduced form of the coenzyme nicotinamide adenine dinucleotide (NADH) (Scheme 4.8) [55], The reaction proceeded according to the Michaelis-Menten kinetics. 

A series of water-soluble calix[n]arenes (n = 4 - 8) with different conformational abilities were investigated as artificial ribonucleases that hydrolyze cytidine-2, 3 -cyclophosphate at pH 2 and 30°C [56]. Best results were obtained with calix[4]arene 12, which inaeased the rate by 16 times (Scheme 4.9). 

SCHEME 4.8 The water-soluble calix[6]arenes 8-11 as catalysts in the hydration of 1,4-di-hydronicotinamide derivatives. (Adapted from Ref. [55] with permission of American Chemical Society. Copyright 1986.)... 

SCHEME 4.11 Structure of the water-soluble calix[4]arene 17. (Adapted from R. [42,62] with permission of American Chemical Society and Elsevier.)... 

Water-soluble calix[n]arenes 20-24 with sulfonated fragments 4-6 aromatic rings) and aminomethylated calix[4]arenes were used as components in the catalytic system for the cross-coupling reactions of l-iodo-4-phenylbenzene and phenylboronic acid (Suzuki reaction) catalyzed by palladium complexes with sulfonated triphenylphosphine (Scheme 4.13) [65], Addition of water-soluble calixarenes increased the yield of reaction products more than twofold. The maximum activity was exhibited by calixarenes containing amino groups 22-24. The appropriate constants of the formation of respective inclusion complexes were significantly higher. 

Shirakawa S, Shimizu S, Sasaki Y. Rhodium-catalyzed biphasic hydroformylation of 4-oc-tene using water-soluble calix[4]arene-phosphine ligands. New J Chem 2001 25(6) 777-9. 

Water-soluble calix[n]arenes are powerful receptors for non-polar substrates in aqueous solution. These compounds are promising candidates as carrier molecules for the transport of non-polar substrates through bulk water as well as inverse phase-transfer catalysts, as proven for the Suzuki coupling of iodobenzene with phenyl boronic acid [91]. 1.5-bis(4,4 -bis(perfluorooctyl)penta-l,4-dien-3-one (39) stabilizes palladium 0) nanoparticles (transmission electron microscopy) formed in the reduction of palladium dichloride with methanol. These palladium colloids are soluble in perfluorinated solvents, and they are efficient recoverable catalysts for Suzuki crosscoupling under fluorous biphasic conditions (Equation 69) [92]. 

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