Allylic esters of TFA-protected amino acids undergo asymmetric Claisen rearrangements in the presence of cinchona alkaloids, giving rise to g,d-unsaturated amino acids in a highly stereoselective fashion. The products are useful precursors for the short and efficient synthesis of more complex compounds such as substituted 4-hydroxyornithines and iminosugars. Starting from the unsaturated amino acids, iodolactonization, bicylization and opening of the lactone ring with nucleophiles such as amino acids or peptides provide hydroxyproline derivatives directly incorporated into peptides.
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diastereoselective syntheses, enantioselective syntheses diastereoselective syntheses, enantioselective syntheses (incl. cis/trans-isomerism) O 0031
-034Asymmetric Chelated Claisen Rearrangements in the Presence of Chiral Ligands -Scope and Limitations.-A variety of chiral amino alcohols and metal salts is investigated in the asymmetric Claisen rearrangement of appropriate glycine esters. Best results are obtained using cinchona alkaloids and Al(O-iPr) 3 . Enantiomeric products can be obtained either by changing the chiral ligand or by changing the reactions conditions using the same ligand (generation of Al-vs. Li-enolates). Ligand acceleration is not observed. -
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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