Resin support reactants

A quaternary ammonium hydroxide ion exchange resin 6 was shown to sequester phenols, hydroxypyrazoles, and other weakly acidic heterocycles.25 The sequestered nucleophiles could also be used as polymer-supported reactants. Similarly, the guanidine-functionalized resin 7 was also shown to be a useful capture agent for weakly acidic nucleophiles, including phenols and cyclic iV-acyl sulfonamides.26... 

Automated synthesis of peptide and oligonucleotide libraries was initiated about 10 years ago [4], Within the last three years, there has been much attention focused on the generation of combinatorial libraries of small molecules. As with biopolymers, the use of solid resin support was central to the advance of this field. In solid-phase synthesis, one of the reactants is covalently bound to the solid support and an excess of the other reactants may be used in each step to drive reactions to completion. Purification of the intermediates and final product is easily achieved through extensive washing of the resin after each chemical step. For the purpose of high throughput synthesis, cleavage of the final... 

There is now an extensive range of supported reactants that use resins, silica, carbons etc, to clean up reactions prior to final purification and is gaining favour in the laboratory. [See section on Scavenger Resins in Chapter 3, at the ends of the sections on Preparation of other adsorbents , FPLC and HPLC .]... 

The basie steps involved in reactions with resin-supported PTC catalysts differ from ordinary two-phase PTC reactions in one important respect ordinary PTC reactions require only one reagent to be transferred from their normal phase to the phase of the second reactant. Use of resin-supported catalysts requires that both reagents diffuse to active PTC sites on the eatalyst surface, or for reactions with slow intrinsic rates, both reagents must also diffuse to the active sites inside the resin bulk phase. The need for diffusion processes with solid catalysts also means that both reagents are required to diffuse to and penetrate the stagnant outer layer of liquid(s) (the Nemst layer), coating the catalyst particle. 

Moberg et al. [146] modified further the bis(pyridylamide) ligand described by Trost for the preparation of a polymer-supported pyridylamide (113 in Scheme 60) for the microwave-accelerated molybdenum-catalyzed al-lylic alkylation. TentaGel resin was tested in the presence of high concentrations of reactants and gave, after a 30 min reaction, total conversion in the... 

The observed distribution can be readily explained upon assuming that the only part of polymer framework accessible to the metal precursor was the layer of swollen polymer beneath the pore surface. UCP 118 was meta-lated with a solution of [Pd(AcO)2] in THF/water (2/1) and palladium(II) was subsequently reduced with a solution of NaBH4 in ethanol. In the chemisorption experiment, saturation of the metal surface was achieved at a CO/Pd molar ratio as low as 0.02. For sake of comparison, a Pd/Si02 material (1.2% w/w) was exposed to CO under the same conditions and saturation was achieved at a CO/Pd molar ratio around 0.5. These observations clearly demonstrate that whereas palladium(II) is accessible to the reactant under solid-liquid conditions, when a swollen polymer layer forms beneath the pore surface, this is not true for palladium metal under gas-solid conditions, when swelling of the pore walls does not occur. In spite of this, it was reported that the treatment of dry resins containing immobilized metal precursors [92,85] with dihydrogen gas is an effective way to produce pol-5mer-supported metal nanoclusters. This could be the consequence of the small size of H2 molecules, which... 

The use of scavenger resins in solution-phase synthesis illustrates a type of procedure that is actually a hybrid between solution-phase and solid-phase methods. The first step of this procedure is clearly a form of solution-phase synthesis since the reactions take place totally within a dissolved state with no solid support provided for any of the reactants. The separation stage of the process occurs only after products have become attached to solid supports—the scavenger resins—from which they may or may not then be removed. 

The epothilone synthesis in Scheme 13.49 has been used as the basis for a combinatorial approach to epothilone analogs. 167 The acyclic precursors were synthesized and attached to a solid support resin by steps A-E in Scheme 13.58. The cyclization and disconnection from the resin were then done by the olefin metathesis reaction. The aldol condensation in step D is not highly stereoselective. Similarly, olefin metathesis gives a mixture of E- and Z-stereoisomers so that the product of each combinatorial sequence is a mixture of four isomers. These were separated by thin-layer chromatography prior to bioassay. In this project, reactants A (3 variations), B (3 variations), and C (5 variations) were used, generating 45 possible combinations. The stereoisomeric products increase this to 180 (45 x 4). 

One research group has exploited the concept of polymer site-isolation in a multistep/one-chamber solution-phase synthesis in which all the reagents, catalysts, and downstream reactants required for a multistep synthesis were combined in one reaction chamber. For instance, a one-chamber/three-step synthesis of substituted acetophenones has been reported (Scheme 10).84 An a-phenethyl alcohol was introduced into a reaction chamber containing the polymer-supported reagents and reactants necessary to accomplish oxidation by polymer-supported pyridinium dichromate 60 bromination by the A-26 perbromide resin 61 and nucleophilic displacement by the A-26 phenoxide resin 62. Filtration afforded the... 

Finally, a five-step solution phase synthesis of benzoxazinones used a combination of reactant-sequestering resins, a bifunctional linking reagent, a polymer-supported reagent, and solid-phase quench for synthesis and purification (Scheme 14)22 This features... 

Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. This research has been conducted in an effort to functionalize a polymer with a variety of different reactive sites for use in membrane applications. These membranes are to be used for the specific separation and removal of metal ions of interest. A porous support was used to obtain membranes of a specified thickness with the desired mechanical stability. The monomer employed in this study was vinylbenzyl chloride, and it was lightly crosslinked with divinylbenzene in a photopolymerization. Specific ligands incorporated into the membrane film include dimethyl phosphonate esters, isopropyl phosphonate esters, phosphonic acid, and triethyl ammonium chloride groups. Most of the functionalization reactions were conducted with the solid membrane and liquid reactants, however, the vinylbenzyl chloride monomer was transformed to vinylbenzyl triethyl ammonium chloride prior to polymerization in some cases. The reaction conditions and analysis tools for uniformly derivatizing the crosslinked vinylbenzyl chloride / divinyl benzene films are presented in detail. 

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