Merrifield-type resins

The alternative strategy for heterogenization has been pursued by Blechert and co-workers, for a polymer-supported olefin metathesis catalyst. A polymer-anchored carbene precursor was prepared by coupling an alkoxide to a cross-linked polystyrene Merrifield-type resin. Subsequently, the desired polymer-bound carbene complex was formed by thermolytically induced elimination of ferf-butanol while heating the precursor resin in the presence of the desired transition metal fragment (Scheme 8.30). 

Scheme 5.5.8 Stannylation of Merrifield type resins with 5- or 6- atom spacers...

Scheme 5.5.9 Stannylation of the Merrifield type resin with a 2C spacer...

For this synthesis a photolabile link-up to a Merrifield-type resin was used. The following summarizes the synthesis, which elegandy combines the advantages of solid-phase synthesis with that of iterative block synthesis ... 

Based on Frechefs work [20], Luis and coworkers [21] studied the influence of the mode of preparation of the polystyrene backbone functionalized with TADDOL (a,a,a, a -tetraaryl-l,3-dioxolane-4,5-dimethanol) 2. This immobilized ligand was loaded with titanium on the topicity of an asymmetric transformation. Here, the Diels-Alder reaction of cyclopentadiene with 3-crotonyl-l,3-oxazolidin-2-one was chosen as a model reaction. The TADDOL ligands were incorporated into the polymeric backbone either by polymerization using functionalized styrene derivative 1 or by grafting and coupling of phenol 2 to Merrifield-type resins (Scheme 7). 

Merrifield-type resins). These resins are fairly cheap, can be easily functionalised with high loading (typically 1-3.5 mmol/g) and are extensively used in solid-supported polypetide- as well as in small molecule synthesis. 

Polystyrene / DVB-crosslinked polymeric matrix coated with polyethyleneglycol spacers of various sizes (e.g. TentaGel ). These resins are less hydrophobic and show better swelling properties in aqueous solutions. They are usually mechanically less stable, more expensive and show a lower degree of loading than the Merrifield-type resins. They find extensive use in solid-supported polypetide and small molecule synthesis. 

Today s chemists can buy Merrifield-type resins with varying degrees of chloromethyl substitution and cross linking tailored for specific purposes. Because the chlorine atom is primary and benzylic, these resins can be further modified by nucleophilic substitution. 

In order to circumvent these limitations, Blossey et al. (1973a) and Schaap et al, (1975) reported the preparation of this photosensitizer covalently bound to Merrifield-type resins via an ester bond (Scheme 13-7). 

Merrifield-type resins are among the most prominent organic supports for solid-phase synthesis, particularly in... 

Other nucleophiles can be chosen to perform substitutions on sulfonate ester linkers. Roush et al. synthesized alkyliodides 542 via cleavage of oligosaccharides from Merrifield-type resins 541 by addition of Nal to the resin-bound substrates [314]. 

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