A new class of asymmetric phase-transfer catalysts derived from Cinchona alkaloids - Application in the enantioselective synthesis of α-amino acids

Tetrahedron Letters

Volumn 38, Issue 49, 1997, Pages 8595-8598

  Lygo, Barry ^a   Wainwright, Philip G ^a  

^a UNIVERSITY OF SALFORD   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

ALPHA AMINO ACID; CINCHONA ALKALOID;

ALKYLATION; ARTICLE; CATALYST; DRUG SYNTHESIS; ENANTIOMER; REACTION ANALYSIS; STEREOCHEMISTRY;

CINCHONA;

EID: 0030659804     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(97)10293-3     Document Type: Article

References (15)

1. For general discussions on the enantioselective synthesis of α-amino acids see: Williams, R.M; "Synthesis of Optically Active α-Amino Acids"; Pergamon Press; New York; 1989.
2. For general discussions on asymmetric phase-transfer catalysis see: O'Donnell, M.J. In "Catalytic Asymmetric Synthesis"; Ed. Ojima, I; VCH; New York; 1993.
3. (a) O'Donnell, M.J; Wu, S; Huffman, J.C. Tetrahderon, 1994, 50, 4507;
4. (b) Tohdo, K; Hamada, Y; Shiori, T. Synlett, 1994, 247;
5. (c) Tohdo, K; Hamada, Y; Shiori, T. Pept. Chem., 1991, 7;
6. (d) Imperiali, B; Fisher, S.L. J. Org. Chem., 1992, 57, 757;
7. (e) O'Donnell, M.J; Bennett, W.D; Wu, S. J. Am. Chem. Soc., 1989, 111, 2353;
8. (f) Esikova, I.A; Nahreini, T.S; O'Donnell, M.J. in "ACS Symposium Series 659: Phase-Transfer Catalysis - Mechanisms and Syntheses", Ed. Halpern, M.E., ACS, Washington D.C, 1997, p89;
9. (g) O'Donnell, M.J; Esikova, I.A; Mi, A; Shullenberger, D.F; Wu, S. in "ACS Symposium Series 659: Phase-Transfer Catalysis - Mechanisms and Syntheses", Ed. Halpern, M.E., ACS, Washington D.C, 1997, p124.
10. 3f that careful manipulation of the reaction parameters can lead to increased enantioselectivity. In this way the alkylation of glycine-imine (1) with benzylbromide using catalyst (5, X=Br) has been improved from 66% e.e. to 81% e.e.
11. Lygo, B; Crosby, J; Lowdon, T.R; Wainwright, P.G. Tetrahedron Lett., 1997, 38, 2343.
12. 6. Unless otherwise stated, the e.e. values were determined by HPLC of the crude imine on a chiral Baker-Bond DNPG (covalent) column, values reported are reproducible to ±2%.
13. 4) and concentration under reduced pressure gives the crude amino acid tert-butyl ester which can generally be purified by passing through a plug of silica.
14. 8. E.e. values were determined by HPLC of the crude N-benzoylamino acid tert-butyl ester on a Chiralcel OD-H column, values reported are reproducible to ±5%.
15. 9. The corresponding alkyl bromides tend to react very slowly. It is also advantageous to use iodine-free alkyl iodides and to carry these reactions out in the dark.