Dendrimer achiral

In 2008, these authors reported a new strategy to attach chiral trans-l-arenesulfonylamino-2-isoborneolsulfonylaminocyclohexane to an achiral Frechet dendron (polyether having a repeated 3,5-dioxybenzyl structure) by a radical approach.The dendrimers obtained were successfully used in the enantioselective nucleophilic alkylation and arylation of ketones, providing... 

The stereogenic centers of chiral dendrimers synthesized so far are either generated by asymmetric synthesis, or they are derived from molecules of the pool of chiral building blocks. The only investigation on chiral dendrimers, consisting of achiral building blocks exclusively, was published by Meijer et al., who synthesized dendrimers such as 31 [61] (Fig. 14). This compound ows its chiral-... 

In 1994 we published the first chiral dendrimers built from chiral cores and achiral branches [ 1,89], see for instance dendrimer 57 with a core from hydroxy-butanoic acid and diphenyl-acetaldehyde and with twelve nitro-groups at the periphery (Fig. 21). As had already been observed with starburst dendrimers, compound 57 formed stable clathrates with many polar solvent molecules, and it could actually only be isolated and characterized as a complex [2 (57- EtO-Ac (8 H20))]. Because no enantioselective guest-host complex formation could be found, and since compounds of type 57 were poorly soluble, and could thus not be easily handled, we have moved on and developed other systems to investigate how the chirality of the core might be influencing the structure of achiral dendritic elongation units. 

Following the convergent procedure, dendrimers of type 58,59 and 60 have been prepared from the chiral core triol 54 and achiral Frechet-type [62] ben-zylic branch bromides. In the series of dendrimers with aromatic spacers (60) and without spacers (58), the optical activity [a]D decreased on going from the 1st (not shown in Fig. 21) to the 2nd generation, whereas with aliphatic spacers... 

To catalyze asymmetric transformations, catalytically active sites can be incorporated in different areas of a dendrimer a) chiral sites at the periphery, b) chiral sites in cavities or at the core, c) achiral sites which are surrounded by chiral branches in the interior of the dendrimer. 

Figure 7. Representative HPLC separations of the stereoisomers of (a) dendrimer 5 (G = 1) at 298 K and (b) dendrimer 6 (G = 1) at 258 K using a HPLC achiral stationary phase of ODS and ACN/THF (55 45) as mobile phase.

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