Dendritic supports in organic synthesis

Study of Hyperbranched Poly(ethyleneimine) Polymers of Different Molecular Weight and Their Interaction with Epoxy Resin

Two different commercial hyperbranched poly(ethyleneimine)s (HBPEI), with molecular weights (MW) of 800 and 25,000 g/mol, and denoted as PEI800 and PEI25000, respectively, as well as the mixtures with a Diglycidyl Ether of Bisphenol-A (DGEBA) epoxy resin, have been studied using thermal analysis techniques (DSC, TGA), dielectric relaxation spectroscopy (DRS), and dynamic mechanical analysis (DMA). Only a single glass transition is observed in these mixtures by DSC. DRS of the HBPEIs shows three dipolar relaxations: γ, β, and α. The average activation energy for the γ-relaxation is similar for all HBPEIs and is associated with the motion of the terminal groups. The β-relaxation has the same average activation energy for both PEI800 and PEI25000; this relaxation is attributed to the mobility of the branches. The α-relaxation peak for all the HBPEIs is an asymmetric peak with a shoulder on the high temperature side. This shoulder suggests the existence of ionic charge trapped in the PEI. For the mixtures, the γ- and β-relaxations follow the behaviour of the epoxy resin alone, indicating that the epoxy resin dominates the molecular mobility. The α-relaxation by DRS is observed only as a shoulder, as a consequence of an overlap with conductivity effects, whereas by DMA, it is a clear peak.

Parallel and combinatorial liquid-phase synthesis of alkylbiphenyls using pentaerythritol support

Unfunctionalized alkylbiphenyls were fabricated by a parallel and combinatorial synthesis using pentaerythritol as a tetrapodal soluble support for a sulfonate-based traceless multifunctional linker system. Nickel N-heterocyclic carbene-catalyzed reactions of pentaerythritol tetrakis(biphenylsulfonate)s with primary alkylmagnesium bromides generated the alkylbiphenyl derivatives by desulfitative cleavage/cross-coupling of the C-S bond without any "memory" of the attachment on the support. Though the reactions were completed with sufficient yields in 12 h at room temperature, even with only 1.5 equiv of nucleophiles, they still retained the benefits of facile isolation observed in polymer-supported reactions.

High-loading polyglycerol supported reagents for Mitsunobu- and acylation-reactions and other useful polyglycerol derivatives

In this paper we present soluble dendritic polyglycerol (PG) supported reagents PG-DEAD, PG-PPh3, and PG-DCC as well as scavengers PG-carbonate, PG-carbazate, and PG-amine, which all have been synthesized in high overall conversions and yields using simple purification techniques. The supported reagents have been used simultaneously in Mitsunobu and acylation reactions. All polymeric reagents and scavengers can be removed by simple precipitation/filtration protocols to give chromatography-free products of high purity. In the course of the syntheses of the polymeric reagents three intermediates turned out to be precious polyglycerol derivatives: a mixed carbonate as an electrophilic derivative, polyglyceryl carbazate as a scavenger for carbonyl compounds, as well as polyglycerylamines as amino analogues of polyglycerol.

Giant dendrimer-like particles from nanolatexes

A straightforward grafting of a polycationic phosphorus-containing dendritic shell onto polystyrene nanoparticles leads to dendronized nanoparticles showing unique behavior.

Dendritic effect in polymer-supported catalysis of the intramolecular Pauson-Khand reaction

A remarkable increase in catalytic activity and selectivity in the intramolecular Pauson-Khand reaction is observed for Co complexes, immobilised on second- and third-generation dendron-functionalized polystyrene, as compared with their analogues on non-dendronized support.