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Asymmetric Control of 1,3‐Dipolar Cycloaddition Reactions with Azomethine Ylides by Means of Proline Esters as Chiral Auxiliary Groups
Author(s) -
Waldmann Herbert,
Bläser Edwin,
Jansen Martin,
Letschert HansPeter
Publication year - 1995
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19950010209
Subject(s) - stereoselectivity , chemistry , triethylamine , diastereomer , cycloaddition , 1,3 dipolar cycloaddition , azomethine ylide , chiral auxiliary , lithium (medication) , proline , hydrolysis , medicinal chemistry , organic chemistry , amino acid , stereochemistry , enantioselective synthesis , catalysis , medicine , biochemistry , endocrinology
Upon treatment with triethylamine or DBU in the presence of LiBr, aromatic and aliphatic imines of amino acid esters are converted to N ‐metalated azomethine ylides. These 1,3‐dipoles undergo highly stereoselective cycloadditions with N ‐acryloyl‐( S )‐proline esters in THF at −78 to −40°C to afford highly substituted pyrrolidines with complete regiocontrol and good to excellent diastereomeric ratios. The chiral auxiliary groups can readily be removed from the cycloadducts by simple acid hydrolysis. To rationalize the observed stereoselectivity a transition‐state model is proposed in which the lithium cation is coordinated to both the 1,3‐dipole and the dipolarophile.