Polymer-supported chemical

Report 52 Polymer Supported Chemical Reactions, P. Hodge, University of Manchester. 

The products of these reactions form the basis for an entire methodology—polymer-supported chemical reactions—wherein the modified polystyrene serves as a reactant, reagent, or catalyst. The reactions are the usual ones of organic chemistry. In the following equation, for example, the modified polystyrene serves as a phase-transfer catalyst (see Section 21.5). The main advantage of using a polymer-supported reagent, or in this case a polymer-supported catalyst, is that it makes isolation of the reaction product easier. 

The N-to-C assembly of the peptide chain is unfavorable for the chemical synthesis of peptides on solid supports. This strategy can be dismissed already for the single reason that repeated activation of the carboxyl ends on the growing peptide chain would lead to a much higher percentage of racemization. Several other more practical disadvantages also tend to disfavor this approach, and acid activation on the polymer support is usually only used in one-step fragment condensations (p. 241). 

There is a large range of resins available for SPOS. These resins are derivatised polymer supports with a range of linkers. The roles of linkers are (i) to provide point(s) of attachment for the tethered molecule, akin to a solid supported protecting group(s), (ii) to provide distance from the polymeric backbone in order to minimise interactions with the backbone, (iii) to enable cleavage of product molecules under conditions compatible with the stability of the molecules and the reaction conditions employed for chemical transformations. Hence in order to... 

Polymer-supported amino alcohols and quaternary ammonium salts catalyze the enan-tioselective addition of dialkylzinc reagents to aldehydes (Table 31). When the quaternary ammonium salt F is used in hexane, it is in the solid state, and it catalyzes the alkylation of benzaldehyde with diethylzinc in good chemical yield and moderate enantioselectivity. On the other hand, when a mixture of dimethylformamide and hexane is used as solvent, the ammonium salt is soluble and no enantioselectivity is observed21. 

This review has shown that the analogy between P=C and C=C bonds can indeed be extended to polymer chemistry. Two of the most common uses for C=C bonds in polymer science have successfully been applied to P=C bonds. In particular, the addition polymerization of phosphaalkenes affords functional poly(methylenephosphine)s the first examples of macromolecules with alternating phosphorus and carbon atoms. The chemical functionality of the phosphine center may lead to applications in areas such as polymer-supported catalysis. In addition, the first n-conjugated phosphorus analogs of poly(p-phenylenevinylene) have been prepared. Comparison of the electronic properties of the polymers with molecular model compounds is consistent with some degree of n-conjugation in the polymer backbone. 

Ley, S.V., Schucht, O., Thomas, A.W., Murray, P.J. (1999) Synthesis of the Alkaloids ( )-Oxomaritidine and ( )-Epimaritidine Using an Orchestrated Multi-Step Sequence of Polymer Supported Reagents. Journal of the Chemical Society Perkin Transactions I, 1251-1252. 

Leznoff CC, Wong JY. The use of polymer supports in organic synthesis. III. Selective chemical reactions on one aldehyde group of symmetrical aldehydes. Can J Chem 1973, 51 3756-3764. 

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