Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 18, Issue 48, Pages 15330-15336Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201201339
Keywords
amino acids; axial chirality; ss-lactams; conjugate addition; protonation
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Funding
- Grants-in-Aid for Scientific Research [23790010] Funding Source: KAKEN
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beta-Lactams with contiguous tetra- and trisubstituted carbon centers were prepared in a highly enantioselective manner through 4-exo-trig cyclization of axially chiral enolates generated from readily available a-amino acids. Use of a weak base (metal carbonate) in a protic solvent (EtOH) is the key to the smooth production of beta-lactams. Use of the weak base is expected to generate the axially chiral enolates in a very low concentration, which undergo intramolecular conjugate addition without suffering intermolecular side reactions. Highly strained beta-lactam enolates thus formed through reversible intramolecular conjugate addition (4-exo-trig cyclization) of axially chiral enolates undergo prompt protonation by EtOH in the reaction media (not during the work-up procedure) to give beta-lactams in up to 97% ee.
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