Highly diastereoselective radical addition to oxime ethers: Asymmetric synthesis of β-amino acids

Organic Letters

Volumn 1, Issue 4, 1999, Pages 569-572

  Miyabe, Hideto ^a   Fujii, Kayoko ^a   Naito, Takeaki ^a  

^a KOBE PHARMACEUTICAL UNIVERSITY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000227151     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol990688o     Document Type: Article

References (42)

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9. Glyoxylic oxime ethers and imines are activated by the adjacent electron-withdrawing substituent.
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13. All radical reactions were run in commercially available solvents and with reagents not requiring any special precautions.
14. For a review on asymmetric synthesis of β-amino acids, see: Cardillo, G.; Tomasini, C. Chem. Soc. Rev. 1996, 117.
15. Among the different types of radical acceptors containing a carbon-nitrogen double bond, oxime ethers are well-known to be excellent radical acceptors because of the extra stabilization of the intermediate aminyl radical provided by the adjacent oxygen atom. See: (a) Miyabe, H.; Torieda, M.; Inoue, K.; Tajiri, K.; Kiguchi, T.; Naito, T. J. Org. Chem. 1998, 63, 4397.
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35. The stereochemical feature of this reaction can be rationalized in terms of stereoelectronic effect in the chelated (Z)-enolate anion as proposed by Oppolzer et al. See reference 11.
36. Full characterization data of all obtained compounds and general experimental procedures are given in the Supporting Information.
37. In general, the signals due to the imino hydrogen of the E-oxime ether are shifted downfield by the influence of the alkoxy group of the oxime ether moiety. See: McCarty, C. G. In The Chemistry of Functional Groups; The chemistry of the carbon-nitrogen double bond; Patai, S., Ed.; John Wiley & Sons Inc.: New York, 1970; pp 383-392.
38. 1H NMR data showed similarity with that of (R,Z)-2a.
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42. 3B acts as a radical initiator and a radical terminator to trap the intermediate benzyloxy radical. Thus, the radical chain reaction proceeds via the regeneration of the ethyl radical by the simple procedure, which does not require the tedious workup to remove the tin residues from the reaction mixture. See refs 4, 6b, and 6c.