Divergent synthetic approaches

The divergent synthetic approach is schematically summarized in Figure 7. Reaction of the mononuclear complex-ligand tRu(2,3-dpp)j] with the complex-metal [Ru(2,3-Medpp)2Cl2] in a 1 3 molecular ratio leads to a tetranuclear complex (first dendrimer generation) which in its peiipheiy contains six protected chelating sites. Demethylation of this species restores its ligand ability and yields... 

Figure 5.1 Schematization of the divergent synthetic approach to buildup dendrimers.

MCRs of up to seven different starting materials have been described in the past [3]. MCRs have numerous advantages over classical approaches (linear, iterative or divergent synthesis) in assembling useful chemical products. The advantage of convergence over a divergent synthetic approach is well appreciated in the syn-... 

FIGURE 15.3 Two most common synthetic strategies for dendrimers. (a) Divergent synthetic approach, (b) Convergent synthetic approach. 

Intra-cellular gel formation with crystalline SAFIN structures is clearly an area of SAFIN research with outstanding potential in future biomedical applications. The decade ahead will likely see gelators with increasing complexity that are designed to assemble and disassemble in the presence of specific biomarkers. Facile and divergent synthetic approaches to peptides derivatives make this field even more attractive. 

Dendrimers are structurally defined branched polymeric molecules and can form good X-ray quality crystals. This is particularly useful in the correlation of structure and properties. Two main synthetic approaches have been used divergent, which is appropriate for smaller dendrimers, and convergent, which is better for larger dendrimers. Branched polysilanes with a structurally defined branched core were described in 1994, but the growth from the core was not controlled and non-uniform structures were obtained.357... 

In order to obtain both series of dendrimers a divergent stepwise synthetic approach was designed. Each generation growth step of this synthetic approach implies four consecutive reactions (a-b) two successive alkylation reactions that... 

Figure 7. Divergent synthetic strategy to obtain polynuclear metal complexes of dendrimer shape. - ° Each deprotected compound of the dive ent synthetic approach can be used as a core in convergent synthetic processes. Some of these routes starting from a tetranuclear core are illustrated in Figure 8.

The first installment in this series (Volume 267, 1996) mostly covered peptide and peptidomimetic based research with just a few examples of small molecule libraries. In this volume we have compiled cutting-edge research in combinatorial chemistry, including divergent areas such as novel analytical techniques, microwave-assisted synthesis, novel linkers, and synthetic approaches in both solid-phase and polymer-assisted synthesis of peptides, small molecules, and heterocyclic systems, as well as the application of these technologies to optimize molecular properties of scientific and commercial interest. 

The simplest synthetic approach to the preparation of monofunctional dendritic systems is to functionalise the periphery of existing molecular scaffolds, generally constructed by divergent or convergent growth (Fig. 3.2, Route a) or b), respectively). 

Kim and Kwon reported the divergent synthesis of a dendritic carbosiloxane from a cyclic siloxane tetramer core130 using the standard carbosilane dendrimer synthetic approach. Allyl alcohol was employed as the nucleophilic reagent and trichlorosilane... 

When faced with the challenge of writing a monograph on the synthesis of imidazoles and benzimidazoles, one is immediately aware that although there are general methods available for the bicyclic compounds, the contrary is true for imidazoles themselves. Indeed, it is necessary to consider a number of widely divergent processes each time a synthesis is contemplated. For this reason I have divided the synthetic approaches arbitrarily into methods which make specific bonds in the imidazole product, those which transform another heterocycle, and those which start with the preformed imidazole ring. 

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