Catalytic Asymmetric Alkylations of Ketoimines. Enantioselective Synthesis of N-Substituted Quaternary Carbon Stereogenic Centers by Zr-Catalyzed Additions of …

P Fu, ML Snapper, AH Hoveyda - Journal of the American …, 2008 - ACS Publications
P Fu, ML Snapper, AH Hoveyda
Journal of the American Chemical Society, 2008ACS Publications
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 α-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 α-amino esters in 79–97% ee. Aryl …
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 α-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 α-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.
ACS Publications
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