Acceptor polymer-supported

Sulfoxide donors have been employed in the glycosylation of soluble and insoluble polymer-supported glycosyl acceptors, and the area has been reviewed [86,283]. 

Scheme 9.2 Comparison of polymer-supported synthesis of oligosaccharides between the attachment of a polymer to a glycosyl donor and a glycosyl acceptor.

Scheme 9.5 Attachment of the succinoyl linker (a) in one step as polymer-supported hemiester (b) in a two-step sequence (a) attaching to the acceptor succinoyl (using succinyl anhydride) first, followed by (b) the attachment of MPEG-OH to the free carboxyl of the succinoyl formed in step a.

Catalyst system comprising a polymer support in which catalytically active species are immobilized through chemical bonds or weaker interactions such as hydrogen bonds or donor-acceptor interactions. 

Thiamine-catalyzed transformations are reversible, thus TV,/V-dialkyl hydrazones were selected as alternative acyl anion equivalents that were reported to react with electrophiles without acidic activation.41 One especially reactive example, formaldehyde hydrazone resin 13, was constructed from polymer-supported hydrazines and was employed in the first polymer-supported, uncatalyzed acyl anion additions (Fig. 8).38 As test substrates, nitroalkenes (as Michael acceptors) and activated aldehydes were selected. Reactivity of these acyl anion equivalents depended critically not only on the nature of the starting hydrazine, but also on the protocol for hydrazine formation. 

Fig. 1. 1,6-Glycosylation with a glucose acceptor attached to a polymer support (P = solid support) and a trichloroacetimidate donor.

Polymer-supported quaternary ammonium hydroxides have been used to catalyse Michael reactions between various alkyl methacrylates, acrylonitrile, and methyl vinyl ketone as acceptors and nitro or keto derivatives as donors.[116,117]... 

Abstract This review covers recent advances in the field of radical chemistry on solid phase. Intermolecular processes using both immobilized radicals with solution-phase acceptors and immobilized acceptors with radicals in solution are discussed, as are radical cyclization reactions on polymer supports. Progress in the development of solid-phase asymmetric radical processes and the design of linkers cleaved by radical processes are also discussed. 

Caddick [19] has reported the use of a novel polymer-supported tetra-fluorophenol-Unked acrylate as an activated acceptor for intermolecular radical reactions. Treatment of immobiUzed acrylate 132 with a variety of alkyl iodides in the presence of tributyltin hydride and AIBN gave the corresponding esters 133 (Scheme 29). NucleophiUc cleavage using amines gave amides 134 in good overall yield whilst regenerating phenol resin 131. 

The slow nucleophilic addition of dialkylzinc reagents to aldehydes can be accelerated by chiral amino alcohols, producing secondary alcohols of high enantiomeric purity. The catalysis and stereochemistry can be interpreted satisfactorily in terms of a six-membered cyclic transition state assembly [46,47], In the absence of amino alcohol, dialkylzincs and benzaldehyde have weak donor-acceptor-type interactions. When amino alcohol and dialkylzinc are mixed, the zinc atom acts as a Lewis acid and activates the carbonyl of the aldehyde. Zinc in this amino alcohol-zinc complex is regarded as a kind of chirally modified Lewis acid. Various kinds of polymer-supported chiral amino alcohol have recently been prepared and used as ligands in dialkylzinc alkylation of aldehydes. 

The polymer-supported methods for removal of the unreacted acceptors during the glyco-sylation process also provide rapid access to automated synthesis and the parallel library synthesis of oligosaccharides. Ley and co-workers applied the polymer-supported tosyl chloride (PS-TsCl) to remove the hydroxyl-containing contaminants, including the acceptors [47]. 

An acylated disaccharide 75 was efficiently prepared using polymer-supported reagents. Formation of glycosyl imidate 72 was carried out with Dowex 1-8X (OH form) as a polymer-supported base, and glycosylation of acceptor 73 with the imidate 72 was carried out using... 

SCHEME 54. Major concepts for the polymer-supported/solid-phase oligosaccharide synthesis glycosyl acceptor bound approach (A) and glycosyl donor bound approach (B). 

Scheme 37. a-(1 2)-mannan synthesis with a polymer-supported acceptor. 

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