Styrenes solid support

The examples listed in Table 3.21 illustrate the synthetic possibilities of cross metathesis. In many of the procedures reported, advantage is taken of the fact that some alkenes (e.g. acrylonitrile, styrenes) undergo slow self metathesis only. Interestingly, it is also possible to realize cross metathesis between alkenes and alkynes (Table 3.21, Entries 11-13), both in solution and on solid supports [927,928]. 

New polymeric solid supports have been devised, which include macroporous styrene-divinylbenzene containing large fixed pores, porous glass beads, insoluble carbohydrate polymers, poly(ethylene oxide), cross-linked derivatives of polyacrylamide resins, and graft copolymers of polystyrene and poly(ethylene oxide). The last two have been the most effective and widely used and have competed well with the original copoly(styrene-divi-nylbenzene) beads. 

Another example of a Pc-based 1-D polymer is that reported by Armstrong and co-workers [158], They prepared a Pc with eight styrene-type polymerizable sites at the end of the peripheral substituents. This molecule forms highly ordered, rod-like aggregates at the air-water interface that can be transferred onto solid supports. Irradiation of the thin films affords polymerization between the olefin moieties of adjacent molecules by photostimulated [2 + 2] cycloaddition. The rod-like Pc macromolecules were conveniently studied by matrix-assisted laser desorp-tion/ionization (MALDI-TOF) spectrometry and atomic force microscopy (ATM), the latter showing rods with lengths up to 290 nm. 

According to our earlier classification, the stationary phase can be a solid, a liquid, or a bonded phase. In the latter two cases, the phase must be coated on, or bonded to, particles of a porous solid support. Only a few materials have found widespread use as stationary solid supports they are silica, synthetic polymers such as the styrene-divinylbenzene copolymer, diatomaceous earths, and some polysaccharides. The most common types and uses are given in Table 2. 

The solid support is a special polystyrene bead in which some of the aromatic rings have chloromethyl groups. This polymer, often called the Merrifield resin, is made by copolymerizing styrene with a few percent of p-(chloromethyl)styrene. 

The solid supports used in this study were macroporous co-polymers of vinylpyridine and styrene crosslinked with divinylbenzene. Polymers of this type in the form of beads are available commercially (e.g. Reillex 425) and were also prepared for this study by Purolite. For spectroscopic studies, a more convenient sample morphology was required and thin-film polymers of similar stoichiometry were synthesised by the group of Sherrington at the University of Strathclyde. Full details of the methods used to prepare thin film polymers are reported elsewhere.11 To generate the ion exchange resin, the pyridyl functionalities of the polymer were quatemised with methyl iodide (Eq 1). 

Merrifield A process for synthesizing peptides, using a solid phase support. The basic process was invented in 1962 by R.B. Merrifield at the Rockefeller Institute for Medical Research, New York, and it was subsequendy automated with the assistance of J. Stewart. The solid supports are chloromethylated copolymers of styrene with divinyl benzene, now commercially available. The process is now widely used commercially for making therapeutic medicines. Merrifield received the Nobel Prize for this work in 1984, which he chose not to patent. 

Various polymeric and solid supports, such as polyethylene glycol (PEG), can be used to immobilise these catalysts.[46 48] Exchanging the polymer support on the styrene moiety for charged ionic liquid tags affords complexes 38 and 39, which are retained to a significantly higher degree in the ionic liquid phase (Scheme 7.4). 

An example of a noncovalent attachment of a metal-phosphine complex to a solid support is presented in Figure 31, as reported by Bianchini et al. (120). The complex is attached via a sulfonated variant of the "triphos" ligand, which is known for its successful application in several catalytic reactions. The ligand is attached to the silica by an ionic bond, which is stable in the absence of water. The catalyst was used for the hydroformylation of styrene and of hex-1-ene in batch mode and showed moderate activity. The triply coordinated rhodium atom is strongly boimd although the conditions were rather harsh (120 °C, 30 bar) the concentration of leached metal measured by atomic emission spectroscopy was at most at the parts per million level. However, for commercial applications, for example, in a process such as hydroformylation of bulk products, these concentrations should be less than 10 ppb 111,121). 

The breakthrough in peptide chemistry, which opened up applications in biochemistry and molecular biology, was the development of solid phase synthesis by Merrifield in 1963. This formed the basis of automated synthetic procedures in which the nascent peptide chain was covalently linked to a solid support such as a styrene-divinylbenzene copolymer the complex isolation and purification procedures needed to separate reactants and products at the end of each reaction cycle, which characterised previous solution methods of peptide synthesis, were replaced by a simple washing step. With modern automated methods of peptide synthesis, the time for an Fmoc reaction cycle has been reduced to 20 min, so that a 50-residue peptide can be synthesised in a day (Chan and White 2000). 

These are, without doubt, the most widely used solid supports. PS systems used for the synthesis of peptides and small molecules consist of 1% cross-linked hydrophobic resins obtained by suspension polymerization from styrene and divi-nylbenzene. For other uses, PS with 2% cross-linking, which is mechanically more stable than those with less cross-linking, is also employed. This 2% PS was used... 

Hence, it did not act as a linker between substrate and polymer. Through a sulfonate (OTs) or benzyl ether linkage the enantiopure imine monomers 47 and 48 were polymerized with styrene under radical conditions. The polymer bound imines 49 and 50 were treated with allyl bromide. Cleavage of the auxiliary followed by detachment from the sulfonate linked solid support, released the desired allylamine 51a in 95% yield with 99% ee. Cleavage of the benzyl ether linkage afforded product 51b in 93-96% yield and 99-100% de. 

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