Calix arenes reactions

Since the first examples of lower and upper rim glycocalixarenes were obtained in 1994 by Marra el al.,106 employing the Mitsunobu reaction or copper(II)-catalyzed glycosylation, the development of efficient synthetic methodologies has allowed the emergence of several examples of ()-, N-, or C-glycosyl calix arenes, and these have recently been reviewed (101-106, Fig. 8).107,10X... 

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.)... 

A study48 of the direct upper-rim alkylation of calix[ ]arenes has shown that, with n = 8, reaction with isopropyl chloride in 1,2-dichloroethane with AICI3 gives isopropylation, whereas when n = 4 hydroxyisopropylation is observed. With n = 6 there is a mixture of products, indicating overall an increase in phenolic behaviour as n increases from 4 to 8. 

Calix[ ]arenes are a family of macrocycles prepared by condensation reactions between n /v/ra-substituted phenols and n formaldehyde molecules under either base or acid catalysis. Different sizes of the macrocycles can be obtained (n = 4-20) (Stewart and Gutsche, 1999) depending on the exact experimental conditions, which were mastered in the 1960 s (Gutsche, 1998), but the most common receptors are those with n =4,6,8 (macrocycles with an odd number of phenol units are more difficult to synthesize). We use here the simplified nomenclature in which the number of phenolic units is indicated between square brackets and para substituents are listed first.4 Calixarenes, which can be easily derivatized both on the para positions of the phenolic units and on the hydroxyl groups, have been primarily developed for catalytic processes and as biomimics, but it was soon realized that they can also easily encapsulate metal ions and the first complexes with d-transition metal ions were isolated in the mid-1980 s (Olmstead et al., 1985). Jack Harrowfield characterized the first lanthanide complex with a calixarene in 1987, a bimetallic europium complex with p-terf-butylcalix[8]arene (Furphy etal., 1987). 

The introduction of nitro groups at the upper rim of calix[4]arenes is a quick and useful method for the preparation of functionalized calix[4]arenes. This reaction is quite general and can be conveniently carried out on a wide variety of calix[4]arenes substituted at the lower rim. When the starting calix-arene is partially substituted at the lower rim, the substitution takes place at the more reactive phenol rings. 

Calix[ ]arenes are a family of macrocycles prepared by condensation reactions between para-substituted phenols and formaldehyde (see Fig. 4.8). In a way, they can be thought... 

Still another route for selective formylation makes use of the tricarbonyl-chromium complexes of calix[4]arenes. Reaction of the tetrapropyl ether of 4 with Cr(CO)3 produces a complex in which a Cr(CO)3 moiety is associated with a single aromatic residue of the calixarene. Treatment of the complex with BuLi and then D2O, Mel, or DMF followed by decomplexation with I2 yields mono-substituted calix[4]arenes carrying D at a p- or m-position. Me at a p-position, and CHO at a p-position, respectively." ... 

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... 

The condensation reaction of dienes with benzaldehydes in the presence of calix[n]arene/Ti(IV) complexes formed in sitn by treating appropriate calix-arenes with Ti(0-t-Pr)4 was stndied [67], and the catalytic effects of the complexes confirmed (Scheme 4.15). 

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). ° ... 

Odd-numbered calix[n]arenes ( = 5, 7, 9) and large calix[ ]arene homologs were also formed by tuning reaction conditions, but owing to the low... 

Scheme 3.2 shows per-functionalized pillar[5]arene derivatives prepared from per-hydro)ylated pillar[5]arene 3.6 as a starting compound. Applying an efficient organic reaction is required for the perfect introduction of functional groups at all 10 reaction sites. A straightforward and efficient functionalization process for per-hydroxylated pillar[5]arene is etherification, which has been used for functionalization of the lower rims of phenolic moieties in calix[ ]arene derivatives. Various functionalized pillar[5]arene derivatives can be obtained by etherification of per-hydroxylated pillar[5]-arene with an alkyl-halide in the presence of appropriate bases, such as NaH and K2CO3. Introduction of the substituents can change various physical... 

Some of calix[ ]arene sulfonic acids were also developed as Bronsted acid catalysts for Mannich-type reactions [23]. Because of their water-solubility, the reaction can be performed in water with obvious advantages from an environmentally point of view. As depicted in Fig. 27.8, two water soluble calixarene bearing a sulphonic acid group are suitably employed in the Mannich reaction in water as a catalyst. 

Silva and collaborators described calixarenes (CAT-30) as efficient catalysts in the Biginelli reaction [41]. They found that the presence of a sulfonyl group on these calixarenes improved their catalytic properties, and the calix-arene CAT-30 showed better results for the preparation of Biginelli adducts than other catalysts (Table 6). They also showed that macrocyclic monomers, in amounts equivalent to CAT-30, resulted in lower efficiency, justifying the use of calixarenes as supramolecular catalysts in these reactions. Aromatic aldehydes were good substrates (yields >52%), while nonaromatic aldehydes were poor substrates (yields >34%). CAT-30 was reused in up to five cycles without any loss of efficiency. 

NaH should serve as an efficient template ion to yield cone conformers. Conformer distribution for the reaction of p-tert-h Wy calix[4]arene and ethyl bromoacetate is given in Table I. 

Table 1 Conformer Distribution for the Reaction of p-Zerz-Butyl Calix[4]arene and Ethyl Bromoacetate [16]...

The azo coupling reaction of the calix[4]arene 12.32 shows an unexpected auto-catalytic effect. If the molar ratio of the diazonium ion (X=N02) to the calix[4]arene is 4 1, the yield of the tetra(arylazo)calix[4]arene 12.33 is 99%, but with ratios 3 1, 2 1, and 1 1 the tetra(arylazo) compound is also a major product (70%, 45%, and 22% respectively). If ratios 3 1, 2 1, and 1 1 are used the yields of the tris- and bis(arylazo) products are in the range of only 1.2-3.4%, and the mono(arylazo) compound is formed with a yield of 5.3-6.0%. Using the ratio 4 1 the bis- and mono(arylazo) products are not found at all, and the tris(arylazo) com-... 

In a closely related study, Marecek et al. [46] used the pendant drop video-image method to investigate the adsorption and surface reactions of calix[4]arene ligands at the ideally polarized water-1,2-dichloroethane interface. The difference between the surface tensions in acidic and alkaline media was ascribed to a difference in the charge on the... 

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... 

The authors synthesized three amino acid substituted calix[4]arenes and investigated their coordination reactions towards Pd11 using electrospray mass spectrometry.384... 

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