Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 130, Issue 16, Pages 5530-5541Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja8001343
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- NIGMS NIH HHS [GM-57212] Funding Source: Medline
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Catalytic enantioselective alkylations of three classes of ketoimines are reported. Reactions are promoted in the presence 0.5-10 mol % of a Zr salt and a chiral ligand that contains two inexpensive amino acids (valine and phenylalanine) and involve Me2Zn or Et2Zn as alkylating agents. Requisite aryl-and alkyl-substituted alpha-ketoimine esters, accessed readily and in > 80% yield on gram scale through a two-step sequence from the corresponding ketones, undergo alkylation to afford quaternary a-amino esters in 79-97% ee. Aryl-substituted trifluoroketoimines are converted to the corresponding amines by reactions with Me2Zn, catalyzed by a chiral complex that bears a modified N-terminus. The utility of the catalytic asymmetric protocols is illustrated through conversion of the enantiomerically enriched alkylation products to a range of cyclic and acyclic compounds bearing an N-substituted quaternary carbon stereogenic center.
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