Dipyrromethane as a new organic reagent for the synthesis of gold nanoparticles: preparation and application

Condensation reaction of several ketones with pyrrole in the presence of ferric hydrogen sulfate as a green homogenous acidic catalyst furnished the corresponding pure dipyrromethanes in good yields. Gold nanoparticles were produced through reduction of HAuCl₄ with substituted dipyrromethanes as new reducing agents at room temperature with the exclusion of any capping agent or surfactant. Gold nanoparticles were characterized by transmission electron microscopy, scanning electron microscopy, XRD and UV–visible absorption spectroscopic measurements. It is proposed that in situ formed oxidative products of dipyrromethane, such as polydipyrromethane could serve effectively as a capping agent to preferably adsorb the {111} facets of gold crystals during the reduction process, which leads to the formation of gold nanoparticles.     

Plasmachemical surface functionalised beads: versatile tailored supports for polymer assisted organic synthesis

Plasmachemical surface modification of porous polystyrene beads with allylamine or diaminopropane provides reactive amine functionality exclusively at accessible surface sites, allowing faster reactions than classically prepared materials.     

Dendrimers and hyperbranched polymers as high-loading supports for organic synthesis

Polymeric supports have become a big necessity for automated synthesis and combinatorial chemistry, yet, the loading capacities of most polystyrene resins are very limited (typically < 1.5 mmol x g(-1)). Dendrimers and hyperbranched polymers have been discussed for this application and now became readily available. These soluble polymers can either be used directly as high-loading supports for substrates, reagents, and catalysts or alternatively in hybrid polymers linked to conventional polystyrene resins.     

The use of polyhedral oligomeric silsesquioxane (POSS) as a soluble support for organic synthesis: A case study with a POSS-bound isocyanate scavenger reagent

The use of polyhedral oligomeric silsesquioxane (POSS) as a soluble support in organic synthesis is reported. A POSS-bound isocyanate was readily synthesised in one step from commercially available starting materials and was isolated in high yield and purity by simple filtration. It was found to perform well as a scavenger for excess amine in the solution phase synthesis of amides and sulfonamides, allowing product isolation in high yield and purity.     

Chiral coordination polymer as a luminescence sensor for small organic molecules

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From polymer to small organic molecules: a tight relationship between radical chemistry and solid-phase organic synthesis

Since Gomberg's discovery of radicals as chemical entities, the interest around them has increased through the years. Nowadays, radical chemistry is used in the synthesis of 75% of all polymers, inevitably establishing a close relationship with Solid-Phase Organic Synthesis. More recently, the interest of organic chemists has shifted towards the application of usual "in-solution" radical chemistry to the solid-phase, ranging from the use of supported reagents for radical reactions, to the development of methodologies for the synthesis of small molecules or potential libraries. The aim of this review is to put in perspective radical chemistry, moving it away from its origin as a synthetic means for solid supports, to becoming a useful tool for the synthesis of small molecules.     

High-load, oligomeric dichlorotriazine: a versatile ROMP-derived reagent and scavenger

A new high-load, soluble oligomeric dichlorotriazine (ODCT) reagent derived from ring-opening metathesis polymerization (ROMP) is reported as an effective coupling reagent, scavenger of nucleophilic species, and activator of DMSO for the classic Swern oxidations. Two variants of this reagent (2G)ODCT 4 and (1G)ODCT 16, possessing theoretical loads of 5.3 and 7.3 mmol/g, respectively, have been synthesized. Preparation was accomplished via simple synthetic protocols affording free flowing powders, amenable for large-scale production. Removal of the spent oligomeric reagent was achieved via either precipitation of the spent reagent or simple filtration utilizing a silica SPE, followed by solvent removal, to deliver products in excellent yield and purity. In addition, the corresponding norbornenyl monomer 3 was successfully demonstrated in a couple-ROMP-filter protocol utilizing in situ polymerization, achieving comparable results versus the corresponding oligomeric variant.     

A new cleavage strategy for ester linked polymer supports: generation of a tertiary alcohol library

The addition of different Grignard reagents to polymer bound esters resulting in the generation of a tertiary alcohol library with concomitant cleavage is described.     

New methods and reagents in organic synthesis. 62 trimethylsilyldiazomethane: A convenient reagent for the preparation of acylsilanes

The lithium salt of trimethylsilyldiazomethane smoothly reacts with alkyl halides to give α-trimethylsilyldiazoalkanes which are easily oxidized with m-chloroperbenzoic acid (m-CPBA), giving the corresponding acylsilanes (α-ketosilanes) in good yields.     

ULTRAMINE: a high-capacity polyethylene-imine-based polymer and its application as a scavenger resin

The synthesis of a novel high-loading polyethylene-imine resin (ULTRAMINE) is described, and its application as a scavenger resin in various acylation reactions is demonstrated. The inverse suspension polymerization technique was used for the synthesis of well-defined spherical polymer beads. Polymer beads with different cross-linking densities were synthesized according to the degree of acryloylation of the polyethylene-imine polymer. The resin was characterized by various spectroscopic techniques. The size, shape, and morphological features of the resin were demonstrated by microscopy. The resin showed excellent swelling properties in both polar and nonpolar solvents. The chemical stability of the resin in various reagents and solvents was investigated and monitored by IR spectroscopy. The mechanical stability of the beads was determined by a single-bead compressive experiment. The ULTRAMINE beads can be used as an excellent scavenger for excess acylating reagent, as demonstrated for a variety of reactions. ULTRAMINE-red resin was derived from ULTRAMINE through exhaustive reduction of the amide carbonyl groups to yield an all-amine resin.     

A simple and convenient method for the preparation of diborane from tetrabutylammonium borohydride and benzyl chloride for application in organic synthesis

Diborane is readily generated in situ at 25 °C in toluene using the Bu₄NBH₄/PhCH₂Cl and Bu₄NBH₄/I₂ reagent systems. The reagent prepared in this way is used for the reduction of carbonyl compounds and hydroboration-oxidation of olefins to obtain the corresponding alcohols in good yields.     

Poly(1,4-butyl-bis-vinylpyridinium) borohydride as a new stable and efficient reducing agent in organic synthesis

The unstable sodium borohydride is stabilized on modified poly(4-vinylpyridinium), and it is used as an efficient and regenerable polymer-supported borohydride reagent for the reduction of a variety of carbonyl compounds, such as aldehydes, ketones, α,β-unsaturated carbonyl compounds, α-diketones and acyloins, in good to excellent yields.     

Exploration of ionic liquids as soluble supports for organic synthesis. Demonstration with a Suzuki coupling reaction

The efficiency of ionic liquid supported synthesis was demonstrated by the Suzuki reaction of ionic liquid supported iodobenzoate compounds with arylboronic acids in aqueous media to give, after cleavage with ammonia/methanol, biaryl products in good yields and high purities, without the need for chromatographic purification. [reaction: see text]     

Parallel synthesis and biophysical characterization of a degradable polymer library for gene delivery

We recently reported the parallel synthesis of 140 degradable poly(beta-amino esters) via the conjugate addition of 20 primary or secondary amine monomers to seven different diacrylate monomers. To explore possible structure/function relationships and further characterize this class of materials, we investigated the ability of each DNA-complexing polymer to overcome important cellular barriers to gene transfer. The majority of vectors were found to be uptake-limited, but complexes formed from polymers B14 and G5 displayed high levels of internalization relative to "naked" DNA (18x and 32x, respectively). Effective diameter and zeta potential measurements indicated that, in general, small particle size and positive surface charge led to higher internalization rates. Of the 10 DNA/polymer complexes with the highest uptake levels, all had effective diameters less than 250 nm and nine had positive zeta potentials. Lysosomal trafficking was investigated by measuring the pH environment of delivered DNA. Complexes prepared with polymers G5, G10, A13, B13, A14, and B14 were found to have near neutral pH measurements, suggesting that they were able to successfully avoid trafficking to acidic lysosomes. This work highlights the value of parallel synthesis and screening approaches for the discovery of new polymers for gene delivery and the elucidation of structure/function relationships for this important class of materials.     

Preparation of new microgel polymers and their application as supports in organic synthesis

A series of soluble microgel polymers have been synthesized using solution-phase polymerization reactions. In a systematic manner, several variables such as monomer concentration, cross-linker content, reaction solvent and reaction time were examined, and this provided an optimal polymer with both solubility and precipitation characteristics suitable for synthetic applications. Thus, a chemically functionalized microgel polymer was synthesized, and the utility of this polymer in the synthesis of a small array of oxazole compounds has been demonstrated. The advantage of the microgel polymers produced was that they exhibited solution viscosities lower than those of conventional linear polymers even at higher concentrations, and this was found to be beneficial for their precipitation properties. Compounds prepared using the described microgel polymer supports were obtained in similar yields and purity when compared with insoluble resins, and more importantly, the soluble polymer bound intermediates could be analyzed at each step using standard NMR techniques.     

Stereoselectivity in ene reactions with 1O2: matrix effects in polymer supports, photo-oxygenation of organic salts and asymmetric synthesis

The ene reaction of chiral allylic alcohols is applied as a tool for the investigation of intrapolymer effects by means of the stereoselectivity of the singlet-oxygen addition. The diastereo selectivity strongly depends on the structure of the polymer, the substrate loading degree and also on the degree of conversion demonstrating additional supramolecular effects evolving during the reaction. The efficiency and the stability of polymer-bound sensitizers were evaluated by the ene reaction of singlet oxygen with citronellol. The ene reaction with chiral ammonium salts of tiglic acid was conducted under solution phase conditions or in polystyrene beads under chiral contact ion-pair conditions. The products thus obtained precipitate during the photoreaction as ammonium salts. Moderate asymmetric induction was observed for this procedure for the first time.