Synthesis of pyrrolidine ring-fused metallofullerene derivatives

The azomethine ylide generated from the reaction of sarconsine and formaldehyde adds to Gd@C₈₂ to give the mono- through octo-adducts, while the direct interaction of sarcosine with Gd@C₈₂ yields only the mono-adduct, which is characterized by HPLC, MALDI-TOF MS, UV-Vis-NIR and FT-IR. The reaction mechanism for this reaction is proposed to be a 1,3-dipolar addition.     

Stereoselective synthesis of polyhydroxylated aminocyclohexanes

The stereoselective synthesis of a series of di- and tri-hydroxylated aminocyclohexane derivatives has been developed. A one-pot, two step tandem process involving an Overman rearrangement and a ring closing metathesis reaction has been utilised for the asymmetric synthesis of (1S)-1-(2',2',2'-trichloromethylcarbonylamino)cyclohexa-2-ene. Oxidation of this cyclohexene derivative was then studied leading to the preparation of two diol analogues in excellent stereoselectivity. (1S)-1-(2',2',2'-trichloromethylcarbonylamino)cyclohexa-2-ene was then converted to a novel allylic alcohol via a 4,5-dihydro-1,3-oxazole. Functionalisation of this allylic alcohol by Upjohn dihydroxylation conditions or by a directed epoxidation/hydrolysis sequence of reactions allowed the synthesis of two dihydroconduramines in excellent stereoselectivity. The stereochemical assignment of all compounds prepared was confirmed by NOE experiments or X-ray structure determination.     

Theoretical investigation of the formation mechanism of metallofullerene Y@C82

The formation mechanism of metallofullerene Y@C82 was investigated by ab initio calculations with two theoretical models. The first model is a traditional Y@C80 + C2 "fullerene-road" growing mechanism, in which the Y@C82 is assumed to form by combining Y@C80 and C2 fragments, and the second model involves formation by an unclosed C76 and a C6Y fragment. The calculated results showed that the second mechanism is much more energetically favorable.     

Synthesis of a nonionic water soluble semiconductive polymer

A new nonionic water-soluble fluorescent conjugated polymer is reported with hydroxyl and amide side chains surrounding an aromatic polymer backbone.     

Synthesis of endohedral metallofullerene glycoconjugates by carbene addition

Endohedral metallofullerene glycoconjugates were synthesized under mild conditions by carbene addition using appropriate glycosylidene-derived diazirine with La(2)@I(h)-C(80). NMR spectroscopic studies revealed that the glycoconjugate consists of two diastereomers of [6,6]-open mono-adducts. The electronic properties were characterized using Vis/NIR absorption spectroscopy and electrochemical measurements. This study demonstrates that glycosylidene carbene is useful to incorporate carbohydrate moieties onto endohedral metallofullerene surfaces.     

Electrochemistry of metallofullerene films: the major isomer of Dy@C82

Solution-cast films of the major isomer of Dy@C(82) (Dy@C(82)(I)) have been studied by cyclic voltammetry (CV) in acetonitrile. The films are found to display pronounced and stable redox responses in solution. The reduction/reoxidation processes exhibit large splittings between the first two reduction and reoxidation waves. However, a pair of reversible oxidation and rereduction waves is observed after the reoxidation of a reduced film. The characteristics and the inter-relationship of these waves are uncovered by the CV technique, scanning electron microscopy (SEM), and UV/Vis-NIR spectra. A possible mechanism is proposed for the film electrode processes, which emphasizes the redox-induced structural reorganization of the metallofullerene film by the incorporation and expulsion of electrolyte ions into and out of the film. The influence of the counter ion diffusivity and the ion-pair stability on the electrochemical activity of the metallofullerene film has also been indicated.     

Improved synthesis of the polyhydroxylated central part of phoslactomycin B

A new approach to the C(7)-C(13) intermediate for the synthesis of phoslactomycin B was investigated. Asymmetric dihydroxylation of the β,γ-unsaturated ester proceeded cleanly to afford the β-hydroxyl-γ-lactone with 97.6% ee, which upon protection as the PMB ether followed by hydride reduction furnished a diol. After selective protection of the prim-OH, oxidation of the sec-OH and chelation-controlled addition of CH₂CHMgBr afforded the C(7)-C(11) segment. Later on, the C(11) stereocentre was constructed by the asymmetric transfer hydrogenation using the Noyori catalyst.     

Resistivity control in the semiconductive region for carbon-black-filled polymer composites

It is known that the electrical volume resistivity of insulating polymers filled with conductive fillers, such as metal particles and/or carbon black (CB) particles, suddenly decreases at a certain content of the filler. Therefore, it is very difficult to control the resistivity in the semiconductive region for the CB-filled composites. We examined two effects to control the electrical volume resistivity in the semiconductive region for CB-filled polymer composites. One is the effect of fluorination of the CB surface on the percolation behavior using surface-fluorinated CB particles as a filler. The other is the effect of copolymerization of polyethylene (PE) with a vinyl acetate (VA) functional group on the percolation behavior using poly(ethylene-co-VA) (EVA) as a matrix. By immersion heat measurements, it was found that the London dispersive component turned out to be the predominant factor of the surface energy of fluorinated CBs. The London dispersive component of the surface energy significantly decreased, while the polar component slightly increased on increasing the fluorine content. The resistivity of fluorinated a CB-filled low-density PE composite showed that the percolation threshold increased, and the transition from the insulating state to the conductive state became sluggish, on increasing the fluorine content. In the case of using EVA as a matrix, on the other hand, the percolation curve was moderated with the increase in the VA content. Therefore, copolymerization of PE with VA is also suitable for the design of a semiconductive polymer composite as well as for fluorination of the CB surface. The total surface area per unit mass of dispersed CB particles in the EVA matrix estimated from small-angle X-ray scattering decreased with increasing CB content. Further, the decrease in the surface area is moderated with an increase in VA content. It was found that the difference in the percolation curve is due to the difference in the dispersive state of CB particles.     

Radical coupling reaction of paramagnetic endohedral metallofullerene La@C82

The thermal reaction of La@C(82)(C(2v)) with 3-triphenylmethyl-5-oxazolidinone (1) in toluene affords benzyl monoadducts La@C(82)(C(2v))(CH(2)C(6)H(5)) (2a-2d). The same monoadducts are also obtained by the photoirradiation of La@C(82)(C(2v)) in toluene without the existence of 1. These reactions are applicable to paramagnetic metallofullerenes, such as La@C(82)(C(s)) and Ce@C(82)(C(2v)). The photoirradiation of La@C(82)(C(2v)) in 1,2-dichlorobenzene in the presence of alpha,alpha,2,4-tetrachlorotoluene also affords the monoadducts La@C(82)(C(2v))(CHClC(6)H(3)Cl(2)) (3a-3d). The monoadducts are fully characterized by spectroscopic analyses. Single-crystal X-ray structure analysis for 3d reveals the unique structure. Theoretical calculations show that the cage carbons having high spin densities are selectively attacked by radical species to form the monoadducts linked by a carbon-carbon single bond. The thermal reaction of La@C(82)(C(2v)) with 1 in benzene affords metallofulleropyrrolidine La@C(82)(C(2v))(C(2)H(4)NCPh(3)) (5), unlike the reaction in toluene.     

Diastereoselective concise syntheses of the polyhydroxylated alkaloids DMDP and DAB

A diastereoselective concise synthesis of the iminosugars DMDP and DAB is presented starting from l-xylose and affording the two alkaloids in good yields of 35% and 22% over seven and eight steps, respectively. The Petasis borono–Mannich reaction of 3,5-di-O-benzyl-l-xylofuranose with benzylamine and (E)-styrylboronic acid served as the nitrogen-introducing key step furnishing the new C–N bond in an entirely diastereoselective manner. A chemo- and regioselective O-mesylation followed by an intramolecular S_N2-cyclisation allowed the formation of the pyrrolidine ring. Ozonolysis of the styryl double bond and subsequent reduction to form the C-5 hydroxymethyl substituent followed by hydrogenolysis of the benzyl protecting groups concluded the DMDP synthesis. Furthermore, an unexpected fragmentation process during the ozonolysis reaction also gave access to the C-5 decarbinolated DMDP derivative DAB.     

Synthesis of polyhydroxylated 7-aminopyrrolizidines and 8-aminoindolizidines

The ammonolysis of a lactone moiety in tricyclic cycloadducts derived from non-racemic five-membered cyclic nitrone and 2(5H)-furanones furnishes an amido function, which after subsequent Hofmann rearrangement, leads to a protected amino group attached to the bicyclic isoxazolidine skeleton. A successive simple transformation, involving cleavage of N-O bond followed by intramolecular N-alkylation, provides an access to the polyhydroxylated 7-aminopyrrolizidines and 8-aminoindolizidines, potential glycosidases inhibitors.     

Synthesis of mono- and polyhydroxylated cyclobutane nucleoside analogs

Enantiomerically enriched cyclobutene compounds 13 and 24 are good precursors of several cyclobutane nucleoside analogs. The synthetic ways involve, in the key step, either hydroboration or dihydroxylation.     

Synthesis of polyhydroxylated xanthones via acyl radical cyclizations

2-Formylphenoxy quinones can be converted into xanthones via an acyl radical intermediate with NBS and AIBN.     

Switchable Solubility of Azobenzene-Based Bolaamphiphiles

The ability to design amphiphiles with predictable solubility properties is of everlasting interest in supramolecular chemistry. Relevant structural parameters include the hydrophobic–hydrophilic balance and structural flexibility. In this work, we investigate the water solubility of azobenzene-based triglycerol bolaamphiphiles (TGBAs). In particular, we analyzed the structural effects of backbone hydrophobicity, flexibility, and cis/trans isomerization on the water solubility of a subset of five TGBAs. This leads to the first example of a non-ionic bolaamphiphile whose water solubility can be changed by irradiation with light. The underlying kinetics were monitored using liquid chromatography and a closer analysis of the underlying aggregation processes provides a mechanistic understanding of the light-driven dissolution process. We anticipate that the results obtained will help to engineer bolaamphiphiles with predictable solution properties in the future.     

Switchable friction of stimulus-responsive hydrogels

Poly(N-isopropylacrylamide) (pNIPAAm) gels are stimulus-responsive hydrogels that exhibit large reversible changes in their volume and surface physicochemical properties near the lower critical solution temperature (LCST) in response to external stimuli, such as a change in temperature or solvent composition. Here we report how different phase states, induced isothermally by changes in the solvent composition, affect the tribological properties of pNIPAAm hydrogels. Our measurements indicate that gels in a collapsed conformation (above the LCST) exhibit significantly more friction than swollen gels (below the LCST) at low shear rates. These differences arise from changes in the surface roughness, adhesive interactions, and chain entanglements of the gel surfaces associated with the phase transition. Importantly, we show that the changes in friction, triggered by an external stimulus, are reversible. These reversible and possibly tunable changes in friction may have a significant impact on the design of coatings for biosensors and for actuation devices based on stimulus-responsive hydrogels.     

Oxidative cleavage of C-Si bonds in polyhydroxylated silacyclopentanes

Oxidative cleavage of C-Si bonds of polyhydroxylated silacyclopentanes under various conditions have led to both the desired polyols and to Peterson elimination products. Further studies on the reactivity of these silacycles, under acidic and basic conditions have been carried out, leading to unexpected results. Treatment of these silacycles under basic conditions thus provided various diols after the cleavage of C_sp³-Si bonds. A mechanistic rationale has been proposed for each case.     

Synthesis of polyhydroxylated aza-bicyclic compounds from sugar allyltins

Highly functionalized polyhydroxylated dienoaldehyde, readily obtained from allyltin and d-glucose, served as a convenient precursor for a variety of configurationally different aza-bicyclic polyols. Such derivatives were deprotected and the activity of these free compounds against glycosidases was also tested.