Stereoselective dendrimers

An interesting example of this kind of stereoselective dendrimer catalysis has been reported by Rico-Lattes et al., who prepared glycoden-... 

The aim of catalyst recycling and the exploitation of possible constructive interactions between catalytic sites underlie the rapidly growing field of stereoselective dendrimer catalysis. Since enantioselection is governed by small increments in the free enthalpy of activation, such transformations are particularly suited to assessing dendrimer effects , which result from the immobilization of catalysts. 

The research group of Van Leeuwen has focused on catalysis at the core of a carbosilane dendrimer in an effort to be able to control stereoselectivity [10]. To this end, a ferrocenyl diphosphine backbone was functionalized with different generations of carbosilane dendrons producing a series of dendrimer phosphine ligands with an increasing steric demand (see 7 for an example, Scheme 6). In situ... 

Fig. 4.70 Dendrocleft (according to Diederich et al.) for stereoselective host/guest interaction depending upon the size of the dendrimer scaffold surrounding the chiral core (marked with a red asterisk)...

Catalytic crossed olefin metathesis can also be used to stereoselectively mono-or bifunctionalise polyolefin dendrimers [6]. Grubbs et al. were already able to... 

Keywords Dendrimers Stereoselective catalysis Homogeneous catalysis Heterogeneous catalysis... 

In water, the highest stereoselectivities were obtained by using the fourth-generation amphiphilic dendrimer, whereas, under heterogeneous reaction conditions in THF as solvent, the third-generation dendritic catalyst proved to be the most selective. 

As has been emphasized at the beginning of this overview of asymmetric den-drimer catalysis, the kinetically controlled stereoselection depends on very small increments of free activation enthalpy. It is therefore an excellent sensitive probe for dendrimer effects and will continue to be studied in this fundamental context. As mono dispersed macromolecules, chiral dendrimer catalysts provide ideal model systems for less regularly structured but commercially more viable supports such as hyperbranched polymers. 

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