enantiomeric excesses and yields. The chiral diether ligand controlled asymmetric conjugate addition of organolithiums to nona-2,7-dienedioates preferentially proceeds via the s-cis conformation with coordination of the carbonyl oxygen atom to the lithium to give a lithium E-enolate intermediate. Subsequent intramolecular conjugate addition of the enolate also proceeds via a cyclic transition state involving
The chiral diether ligand-controlled asymmetricconjugateaddition of organolithiums to nona-2,7-dienedioate and subsequent intramolecular conjugateaddition of the enolate intermediate gave all-trans trisubstituted cyclohexanes with high ee and yields. Using this methodology, an efficient short asymmetric total synthesis of (+)-β-lycorane was accomplished in 33% overall yield through five steps from
Cyclic β-amino acid derivatives: synthesis via lithium amide promoted tandem asymmetric conjugate addition–cyclisation reactions
作者:Stephen G. Davies、David Díez、Sara H. Dominguez、Narciso M. Garrido、Dennis Kruchinin、Paul D. Price、Andrew D. Smith
DOI:10.1039/b500223k
日期:——
skeleton facilitates, after conjugate addition and intramolecular enolate cyclisation, the asymmetric construction of piperidines in high de; variation in the N-protecting group indicates that the highest stereoselectivity is observed with alpha-branched N-substituents. Tandem conjugate addition-aldol reactions can also be achieved stereoselectively, with lithium amide conjugate addition to epsilon- and