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Enantiomeric Enrichment of Allenedicarboxylates by a Chiral Organoeuropium Reagent

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journal contribution
posted on 13.06.1997, 00:00 by Yuji Naruse, Hidefumi Watanabe, Yasuhiro Ishiyama, Tomoe Yoshida
Complexation of dimethyl penta-2,3-dienedioates to tris[(R)-(1R*)-3-(2,2,3,3,4,4,4-heptafluoro-1-oxobutyl)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-onato-O,O‘]europium, (+)-Eu(hfc)3, enriched the (S)-isomer with high enantioselectivity. When a more bulky ester was used, although the enantioselectivity increased to >95% ee, considerable decomposition occurred. Among the available lanthanide shift reagents, only the europium reagent is effective in this transformation. The reaction involves interconversion of diastereomeric complexes, with enrichment of the preferred one. However, the observed decrease in the 1H NMR peaks might suggest that subsequent reconstruction or reordering the higher-order complex may occur in the reaction solution.