Divergent synthesi

J.M.J. Frechet (C. J. Hawker, 1990) replaced the divergent synthesis by a convergent growth of a dendritic polymer. The repeatedly employed monomer, 5-hydroxymethyl-l, 3-benzenediol, was 1,3-O-dibenzylatcd with 3,5-bis(benzyloxy)benzyl bromide. The resulting benzyl alcohol containing 7 benzene rings was converted to the benzyl bromide which was... 

The first steps of a second process for divergent synthesis of dendritic polymers by ATRP are shown in Scheme 9.73.12S In this case, a caiixarcnc core... 

Scheme 10 Divergent synthesis of 2-amino-1,3,4-oxadiazoles and 2-sulfonamido-l,3,4-oxadiazoles...

A divergent synthesis of tropane alkaloid ferruginine was reported by Node and coworkers [59]. The P-ketoester intermediate was prepared by a novel PLE-catalyzed asymmetric dealkoxycarbonylation (hydrolysis followed by a decarboxylation) of a symmetric tropinone-type diester (Figure 6.12). Dimethyl sulfoxide was added to the phosphate buffer pH 8 (1 9) to reduce the activity of PLE and prevent over-deal-koxycarbonylation leading to tropinone. 

Scheme 13. Divergent synthesis of platinum-acetylide dendrimers...

Scheme 3.25 Improved efficiency through divergent synthesis.

Scheme 2. Tomalia s divergent synthesis of dendronized polyethylene imine (PEI)...

Keywords Macromolecules m Dendrimers m Fractal Structure m Hyperbranched Polymers m Nanostructure m Divergent Synthesis m Convergent Synthesis m Dendrylation... 

Dendritic growth hybrids are prepared using one or more functional groups of a preformed linear chain to effect the stepwise growth of one or more dendritic blocks via divergent synthesis. 

At the center of the dendrimer is the core that represents the first synthetic step in divergent synthesis, or the last step in convergent synthesis. Each concentric shell of branched units is a generation (X), designated (GX), of identical repeat units. Hundreds of chemical repeat units have been reported [3, 4], but our characterization has been focused primarily on poly(amidoamine) (PAMAM), -(CH2CH2CONHCH2CH2N) < [1], or poly(propyleneimine)... 

Tomalia, D. A. and Dvornic, P. R. Dendritic polymers, divergent synthesis (starburst polyamidoamine dendrimers) , in Salamone, J. C. (ed.), Polymeric Materials Encyclopedia, Vol. 3, CRC Press, Boca Raton, FL, 1996, pp. 1814-1830. 

We have recently developed a novel, highly efficient, divergent synthesis [25]... 

DIVERGENT SYNTHESIS OF PAMAM DENDRIMERS VIA EXCESS REAGENT METHOD PREPARATION OF ESTER TERMINATED PAMAM STAR-BRANCHED PRECURSOR [NH2-(CH2)2 6-NH21 (G = -0.5) STAR-PAMAMICO E) [1]... 

Scheme 3. Divergent synthesis of the polyphenylene dendrimers based on the Diels-Alder cycloaddition... 

For the divergent synthesis, the reaction sequence is amidification/chlorida-tion. Once the polychloride of the acid is obtained, a partial or total amidifica-tion reaction with an amino alcohol yields a MIM, which is either ionic or nonionic, respectively. 

Fig. 2-22 Divergent synthesis of PAMAM dendrimer. Generation is 1 for LXIV and 5 for LXV.

Goodman and co-workers177-3 have approached the divergent synthesis differently. In their syntheses of collagen models consisting of three copies of homomeric peptide chains, solid-phase schemes begin with monomers 44 and then the template, the Kemp tricarboxylic acid (KTA) 10,[80 is used to link three monomers, also on resin, to form the peptide dendrimers 46 via 45 (Scheme 12). 

Difficulties that have been encountered in divergent synthesis can be attributed to the clustered nature and sequences of peptide dendrimers that form interchain hydrogen bonds and occlude coupling reactions. Solvent combinations such as DMSO and NMP, as well as coupling at elevated temperatures (50-60 °C),[94] have been used to overcome these side reactions and should be used if a single coupling fails to complete the reaction. It is best not to dry the peptide resin at any stage of the synthesis because re-solvation of dried peptide dendrimer resin is difficult. 

---