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Selective modification of the inner surface of halloysite nanotubes (HNTs) by the cycloaddition of azides and alkynes (click reaction) was successfully achieved. Fourier transform infrared spectroscopy and thermogravimetry confirmed that the modification involved only the HNT cavity. Morphological investigations evidenced that the functionalized nanotubes formed microfibers and clusters in the micrometer range. By means of the casting method, these nanomaterials were dispersed into biopolymeric matrixes (chitosan and hydroxypropyl cellulose) with the aim of obtaining nanocomposite films with tunable properties from the physicochemical viewpoint. For comparison purposes, we also characterized composite nanomaterials based on pristine halloysite. The mesoscopic structure of the nanocomposites was correlated with their tensile, thermal, and wettability properties, which were found to be strongly dependent on both the nature of the polymer and the HNT functionalization. The attained knowledge represents a basic point for designing new hybrid nanostructures that are useful in specific purposes such as biocompatible packaging.

The reactions beetwen 2,4-disubstituted thiosemicarbazides and orthoesters in refluxing xylene led to the formation of the 1,2,4-triazoline-5-thione ring and to the 1,2,4-triazolium-5-thiolate ring. The formation of the mesoionic componds is due to rearrangement of the easily available 2,4-disubstituted thiosemicarbazides to 1,4-disubstituted thiosemicarbazides under the reaction conditions adopted. This method can be usefully used for the synthesis of mesoionic compounds, especially in the case of the 2-methyl-4-phenylthiosemicarbazide.

The behaviour towards gas-phase protonation of a series of 2,6-dimethyl-4-X-acetophenones DM1 exhibits strong similarities with that of the corresponding 4-X-acetophenones 1 . A comparison with previous basicity data in solution and AM1 semiempirical calculations suggest that the X-dependent rotation of the probe group out of the plane of the aromatic ring caused by the two ortho methyls is of minor importance in influencing the substituent effect on the gas-phase basicity of DM1 ; on the contrary, it could heavily affect the solvatability and thus be responsible for the observed behaviour of DM1 in strongly acidic media.

In this perspective article the “release and catch” catalytic system concept is discussed. A “release and catch” catalytic system is prepared by non-covalent immobilization of the catalytic moiety on a suitable support, but differently from the usual non-covalently supported catalyst, the catalytic moiety is released in solution over the course of the reaction and it is recaptured at the end of the reaction. Such a “catalyst-sponge like” or “boomerang” system allows one to combine the benefits of homogeneous and heterogeneous catalysis and can be applied to organometallic-based catalysts, organocatalysts and metal-based catalysts.

Steric interactions between aryl and heterocyclic moieties in 2-substituted-2,3-dihydro-3-o-tolyl(chlorophenyl)-4(1H)-quinazolinones 1a-j produce sufficient restriction to rotation about the aryl CN bond that the presence of torsional isomers may be detected at room temperature. Diastereomeric population and free energy of activation for rotation have been calculated by 1H nmr spectra. Probably due to a preferred axial position of R2 substituent no dramatic variation both in A/B ratio and in ΔG≠ value has been observed for 1a-f. The comparison between 1a and 1j ΔG≠ values allows to formulate a hypothesis on the structure of the transition state.

The gelling ability of some geminal imidazolium salts was investigated both in organic solvents and in water solution. Organic salts differing either in the cation or anion structure were taken into account. In particular, the effects on the gel-phase formation of isomeric substitution on the cation or anion as well as of the use of mono- or dianions were evaluated. As far as the cation structure is concerned, isomeric cations, such as 3,3′-di-n-octyl-1,1′-(1,4-phenylenedimethylene)diimidazolium and 3,3′-di-n-octyl-1,1′-(1,3-phenylenedimethylene)diimidazolium, were used. On the other hand, in addition to the bromide anion, isomeric dianions, such as the 1,5- and 2,6-naphthalenedisulfonate anions, were also examined. After preliminary gelation tests, different factors affecting the obtained gel phases, such as the nature of the solvent, organogelator concentrations, and action of external stimuli, were analyzed. The gel-phase formation was also studied as a function of time, by using resonance light scattering measurements. Gel morphologies were analyzed by scanning electron microscopy. To further support the understanding of the different behavior shown by the isomeric cations, some representative ion pairs were analyzed by DFT-based investigations. The collected data underline the significant role played by isomeric substitution of both cation and anion structures in determining the gelling capability of the investigated salts, as well as the properties of the gel phases. Finally, DFT investigations were helpful in the identification of the structural features affecting the self-assembly.

Bis(imidazolium)-tagged 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) catalysts were adsorbed on different supports such as silica gel, silica gel modified with highly cross-linked polymeric imidazolium networks, and highly cross-linked polymeric imidazolium networks entrapping magnetic particles. These systems provided a convenient tool for the oxidation of both primary and secondary alcohols working as recyclable reservoirs for the bis(imidazolium)-tagged TEMPO catalysts. By using EPR spectroscopy it was demonstrated that the catalyst was released as the corresponding oxoammonium salt in the solution during the recycling step, thus promoting the oxidative process in a homogeneous fashion. After solvent removal, the catalyst was readsorbed on the support allowing an easy recovery and recycle of the catalytic material up to 13 consecutive cycles with no loss in activity. The bis(imidazolium)-tagged TEMPO catalyst could be used in only 1mol% both for the oxidation of benzylic and aliphatic alcohols. The catalytic material was highly recyclable if used on silica or imidazolium-modified silica gel in 10mol% loading. Loading could be scaled down to 1mol% and the catalyst proved to be recyclable up to 8cycles only with imidazolium-modified silica gel. Such a "catalyst-sponge-like" system permits to combine the benefits of homogeneous and heterogeneous catalysis. Catch and release: Why spend money on covalent immobilization or ionic liquids with bulky cations? A bis(imidazolium)-modified 2,2,6,6-tetramethylpiperidine 1-oxyl catalyst can be adsorbed on an imidazolium-modified support, then released in the presence of a proper organic solvent and recaptured at the end of the reaction on removal of the solvent

In this perspective article the “release and catch” catalytic system concept is discussed. A “release and catch” catalytic system is prepared by non-covalent immobilization of the catalytic moiety on a suitable support, but differently from the usual non-covalently supported catalyst, the catalytic moiety is released in solution over the course of the reaction and it is recaptured at the end of the reaction. Such a “catalyst- sponge like” or “boomerang” system allows one to combine the benefits of homogeneous and heterogeneous catalysis and can be applied to organometallic-based catalysts, organocatalysts and metal-based catalysts.

A new class of functionalised dicationic ionic liquids, containing a central cationic unit capped by a basic functionality (imidazole), has been synthesised. These salts have been characterised in isotropic solution using proton and 2D-NMR spectroscopy, and their thermal stability has been studied by DSC and TGA. All these novel salts contain the 1-(1-imidazolylmethyl)-3,5-di{1-(3'-octylimidazolylmethyl)}-benzene cation as a defining structural motif. Salts of both singly and doubly charged anions were prepared and, in particular, the selected monoanions (Br(-), [BF4](-), or [NTf2](-)) differ in size, shape and hydrogen-bonding ability, whereas the dianions differ in the nature of the spacer, such as 1,4-benzenedicarboxylate, 2,6-naphthalenedicarboxylate, 1,5- and 2,6-naphthalenedisulfonate, 1,4-butanedicarboxylate, and 1,6-hexanedicarboxylate. These ionic liquids exhibit the presence of different conformers in solution, whose distribution is affected by the nature of the anion. The nature of the anion also affects their thermal stability.

Treatment of benzaldehyde semicarbazones 1a-i with cupric perchlorate in acetonitrile at 40 provided selectively the corresponding 1,2,4-triazolin-5-ones 2a-i. The relative rate constants for 2a-i formation were determined by the competitive method. The results obtained showed that electron-donating substituents (methyl and methoxy) increase the reaction rate, while the reverse was found for electron-withdrawing substituents (chloro and nitro group). The reactivity data are discussed on the grounds of two possible mechanisms.

Here we describe for the first time a sequential Suzuki/asymmetric aldol reaction. Such sequential approach was achieved through the combined use of an ionic liquid supported palladium catalyst and the organocatalyst trans-4-(2,2-diphenylacetoxy)proline. Suzuki and asymmetric aldol reactions were performed under aqueous conditions. The use of a palladium catalyst under basic conditions allowed also the first example of sequential Suzuki/Knoevenagel reaction. Reactions were carried out under aqueous conditions and products were isolated in good to high yields and, in the case of the Suzuki/aldol reaction, with diastereoselectivities up to 91:9 and enantioselectivities up to at least 99 %.

Asymmetric organocatalysis is now recognized as the third pillar of asymmetric synthesis. Recent years have witnessed increasing interest towards the use of highly active and stereoselective organocatalysts. This critical review documents the advances in the development of chiral organocatalysts which are systematically used in ≤3 mol% loading in all the sub-areas of the field, namely aminocatalysis, Bronsted acids and bases, Lewis acids and bases, hydrogen bond-mediated catalysis, phase transfer and N-heterocyclic carbene catalyses (194 references).

This chapter is organized in three sections (see Figure 10.1 ): 2. Immobilization of ionic liquids and organocatalysts 2.1 Covalently attached “ ionic liquid ” moieties as supports 2.2 Covalently attached “ ionic liquid ” moieties as linkers 2.3 Covalently attached “ ionic liquid ” moieties as organocatalysts

Rate constants for the mononuclear rearrangement (MRH) of Z -phenylhydrazones of some 5-substituted-3-benzoyl-1,2,4-oxadiazoles in water have been measured in the presence of zwitterionic micelles. The use of micellized N -tetradecyl- N , N -dimethylamineoxide (C 14 DMAO) as the reaction medium allowed to solubilize the otherwise water-insoluble oxadiazoles. Micellar rate effects were analyzed by using a simple pseudo-phase model and compared with those obtained in non-ionic micelles (Triton X-100). Evidence that both the rate of the rearrangement reaction and the binding of the substrates to the micelles are mainly governed by substrate hydrophobicity is obtained. The disagreement with the primarily sterically controlled MRH in Triton X-100 micelles highlights large and intriguing differences between the two micellar environments.

The gelling behavior of some geminal diimidazolium salts was investigated in solvents differing in polarity and hydrogen bond donor ability. The used salts, namely the 3,3'-di-n-decyl-1,1'(1,4-phenylenedimethylene)diimidazolium dibromide [p-Xyl-(decim)(2)][Br](2) (1), the 3,3'-di-n-dodecyl-1,1'(1,4-phenylenedimethylene)diimidazolium dibromide [p-Xyl-(dodecim)(2)][Br](2) (2), and the 3,3'-di-n-dodecyl-1,1'(1,4-phenylenedimethylene)diimidazolium ditetrafluoroborate [p-Xyl-(dodecim)(2)][BF(4)](2) (3), differ in the alkyl chain length and in the anion properties, such as size, shape, and coordination ability. In all cases in which gelation process was observed, the obtained gels were characterized by gel melting temperature determination, resonance light scattering, and UV-vis measurements. On the whole, the investigation allowed to get information about both the thermodynamic stability and the features of the aggregates characterizing the soft materials at the equilibrium. Data collected by us point out that the used organic salts are able to behave as both hydro- and organogelators. In particular, bromide salts formed hydrogels in the presence of α-cyclodextrin allowing to hypothesize that the gelation process is favored by the formation of supramolecular assemblies. To verify this hypothesis, 1D and 2D (1)H NMR measurements were carried out. Both the alkyl chain length and the anion ability to reticulate the three-dimensional network proved to be determinant factors in affecting the gelation process as well as the features of the gel phases. Finally, with the future aim to use the obtained gels as reaction media, the effect of a guest molecule such as the UV-vis active probe Nile Red was studied.

L’allosite (Al2Si2O5•2H2O), è un alluminosilicato naturale, chimicamente simile al caolino; essa ha una struttura tubolare cava dell’ordine dei micrometri (0.5-1 μm ) e un diametro interno dell’ordine dei nanometri (15 nm ). I nanotubi di allosite (HNT) presentano sulla superficie esterna gruppi SiO2 mentre su quella interna gruppi AlOH. Viste le caratteristiche strutturali, HNT trovano applicazioni come Host, fungendo in alcuni casi da nanoreattori. Tali applicazioni sono però limitate dall’idrofilia della superficie, sia interna che esterna. In questo lavoro è stata sviluppata una nuova metodologia sintetica che prevede l’ultilizzo delle microonde per ancorare organosilani come precursori di materiali per successive modifiche con opportune molecole organiche come ad esempio, nel nostro caso, Liquidi Ionici (IL).

Here we describe for the first time a sequential Suzuki/asymmetric aldol reaction. Such sequential approach was achieved through the combined use of an ionic liquid supported palladium catalyst and the organocatalyst trans-4-(2,2-diphenylacetoxy)proline. Suzuki and asymmetric aldol reactions were performed under aqueous conditions. The use of a palladium catalyst under basic conditions allowed also the first example of sequential Suzuki/Knoevenagel reaction. Reactions were carried out under aqueous conditions and products were isolated in good to high yields and, in the case of the Suzuki/aldol reaction, with diastereoselectivities up to 91:9 and enantioselectivities up to at least 99 %.

With the aim of the synthesis of chemically modified cyclodextrins bearing polyamine pendant groups, potentially useful as capping agents for the preparation of nanosized metal systems or as auxiliaries for gene transfection, the reaction between the heptakis-(6-iodo)-(6-deoxy)-b-cyclodextrin and various polyamines has been explored. This synthetic approach allows obtaining materials constituted by mixtures of cyclodextrins, having different degrees of substitution, which were satisfactorily characterized by means of various complementary techniques (ESI-MS, NMR, potentiometric titration). The products obtained were successfully subjected to preliminary tests for their binding abilities towards suitable organic guests and as capping agents for the preparation of stable silver nanoparticles.

Microwave irradiation was successfully used in order to obtain stable supramolecular aggregates between cyclodextrins and cucurbiturils, without the participation of any long-chain common ‘molecular thread’ guest. These aggregates were characterised by means of various different techniques, namely NMR, thermogravimetry, polarimetry and ESI-MS. Cross-analysis of experimental data allowed us to obtain insights on the stoichiometries of the composites and their thermal stabilities. The possible structures of the composites are briefly discussed, as well as the actual nature of their intrinsic stability.

The dichotomic nature of ionic liquids (ILs, simple solvents or supramolecular fluids) induced us to carry out a structural investigation of some mono-and dicationic ionic liquids using 1D and 2D NMR, resonance light scattering, and UV/Vis spectroscopy. Ionic liquids with different cation π-surface areas were used, namely [bmim][NTf2], [Bzmim][NTf 2], [Bzbim][NTf2], [p-Xyl-(bim)2][NTf 2]2, and [m-Xyl-(bim)2][NTf2] 2 [bmim = 1-butyl-3-methylimidazolium, Bzmim = 1-benzyl-3- methylimidazolium, Bzbim = 1-benzyl-3-butylimidazolium, NTf2 = bis(trifluoromethansulfonyl)imide]. In order to verify to what extent the structural investigation, coupled with the determination of solvent parameters, could help to rationalize the effects of the solvent media on a given reaction, the thermally induced mononuclear rearrangement of heterocycles was studied. Variation of the cation structure has significant repercussions on the 3D structure of the ILs and on the effect they can exert on a given reaction.

The oxidative cyclization of some aldehyde semicarbazones 10 with four different oxidizing agents has been effected. The structure of the semicarbazones and the nature of cyclizing agent affected the rate and yield of cyclization but they did not show any influence on the regiochemistry of reaction. In fact, 1,2,4-triazoline 20 was the only heterocyclic ring obtained by the cyclization reaction.

The sol-gel entrapment of chromium(VI) within a silica matrix, obtained by oxidation with ozone of the corresponding entrapped chromium(III), was found to be an efficient and recyclable oxidizing system (at least up to 16 times) for benzylic alcohols. No leaching of chromium in solution was observed, which prevented any environmental pollution.

The stereoselective rearrangement of tetrahydrofuran or tetrahydropyran rings having a phenylsulfanyl group in an exo position, via the intermediate thiiranium ions, is reported. The 5- or 6-exo-tet cyclization of hydroxy sulfides gave the kinetic products while the 6-endo-tet or 5-endo-tet gave the thermodynamic products. The rearrangement of the 5-exo product to the 6-endo- one is an interesting way for the stereoselective synthesis of substituted tetrahydropyrans.

High selectivities (93–99%) and excellent stereoselectivities (>99%) in the semihydrogenation of CC triple bonds were achieved using palladium on pumice with a metal loading of 0.5, 1.5 or 3.0% wt as catalyst. The reactions were carried out in ethanol or tetrahydrofuran with only 2.5% of ethylenediamine allowing a self-terminating semihydrogenation independently on the CC triple bond.

Stereoselectivity, regioselectivity and yields in the 6-exo selenoetherification of four unsaturated diols were found to depend on the stereochemistry of the diols and on the presence of an oxygen atom close to the intermediate seleniranium ring. Silica gel was useful in order to obtain good yields. Reactions performed both under kinetic and thermodynamic control led to the same products. Stereoselectivity, regioselectivity and yields in the 6-exo selenoetherification of four unsaturated diols were found to depend on several factors such as the stereochemistry of the diols, the nature of the R group, the nature of the counter anion of the PhSe+ species and the presence of silica gel.

The protonation of some 5-substituted 3-nitro-2-pyrrolidin-1-ylthiophenes 1C and 3-substituted 5-nitro-2-pyrrolidin-1-ylthiophenes 2C in aqueous perchloric acid has been studied. The modified Hammett, Bunnett–Olsen and Marziano–Cox–Yates methods have been used to calculate pKBH+ values, which have been correlated with substituent effects. Furthermore, the protonation of pyrrolidin-1-ylthiophenes 1C and 2C has been compared with that of the corresponding N,N-di-methylamino-(1A and 2A) and piperidin-1-yl-thiophenes (1B and 2B). The results have been interpreted on the grounds of the different interactions occurring between the amino group at C-2 and the nitro group or variable substituent at C-3.

The reactivity of aldehyde thiosemicarbazones 1 with ferric chloride solutions was examined. When compounds 1 are not substituted on the N-2 nitrogen atom formation of 1,3,4-thiadiazole 3 heterocyclic ring was observed. In contrast 1,2,4-triazoline 4 and/or 1,3,4-thiadiazoline 5 heterocyclic rings were afforded when N-2 nitrogen atom carried a methyl or a phenyl group. The reaction mechanism is also discussed.

The photochemical behaviour of some substituted aldehyde thiosemicarbazones 1a-k has been investigated in methanol at 254 nm. Thiosemicarbazones of glyoxil methyl ester 1a-f cyclized to furnish the 3-thioxo- 1,2,4-triazin-5-one 2 ring system. The remaining thiosemicarbazones 1g-j gave 1,2,4-triazoline 4 derivatives.

The oxidative cyclization of some aldehyde semicarbazones 10 with four different oxidizing agents has been effected. The structure of the semicarbazones and the nature of cyclizing agent affected the rate and yield of cyclization but they did not show any influence on the regiochemistry of reaction. In fact, 1,2,4-triazoline 20 was the only heterocyclic ring obtained by the cyclization reaction.

Within the framework of research carried out on the behaviour of ArCOY compounds the title reaction has been investigated in order to gain information on the influence of Ar and of Y on the interaction between Y and CO and between Ar and CO, respectively, when Ar = 4-substituted phenyl and Y = 5-substituted thiophen-2-yl. The pKBH+ values collected in this work have been analysed by linear free energy relationship and the calculated p values (0.98 and 2.15 for substitution in the phenyl group and thiophen-2-yl ring, respectively), as well as the mean value (0.97) of m*, have been compared with those of 5-substituted-2-acetylthiophenes 2 and 4-substituted acetophenones 3. From the above comparisons we conclude that solvation has a role, as important as that of the electronic density on the basic centre, in determining the degree of protonation of weak bases even if they are structurally similar.

An efficient regiochemical control in the synthesis of tetrahydrofurans was achieved by acid-catalyzed cyclization of hydroxy-selenides ( 10a ) and ( 11a ) which cyclize in the endolexo mode and by hydroxy-sulfides ( 10c ) and ( 11c ) which cyclize in the exo mode. By cyclization of the relevant hydroxy-selenides, the C15–C20 fragment of (+)-Rolliniastatin 1 was obtained. Semiempirical calculations (PM3) were used in rationalizing experimental results.

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High selectivities (93–99%) and excellent stereoselectivities (>99%) in the semihydrogenation of CC triple bonds were achieved using palladium on pumice with a metal loading of 0.5, 1.5 or 3.0% wt as catalyst. The reactions were carried out in ethanol or tetrahydrofuran with only 2.5% of ethylenediamine allowing a self-terminating semihydrogenation independently on the CC triple bond.

Stereoselectivity, regioselectivity and yields in the 6-exo selenoetherification of four unsaturated diols were found to depend on the stereochemistry of the diols and on the presence of an oxygen atom close to the intermediate seleniranium ring. Silica gel was useful in order to obtain good yields. Reactions performed both under kinetic and thermodynamic control led to the same products.