- ALKYLATION AND PROTONATION OF CHIRAL SCHIFF BASES: DIASTEREOSELECTIVITY AS A FUNCTION OF THE NATURE OF REACTANTS
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The factors controlling the diastereoselective alkylation and protonation reactions of chiral Schiff bases prepared from 2-hydroxypinan-3-one and α-aminoesters are reported: nature of the ester, of the alkylating agent and of the base.
- Tabcheh, Mohamed,Achqar, Abdelrhani El,Pappalardo, Louis,Roumestant, Marie-Louise,Viallefont, Philippe
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p. 4611 - 4618
(2007/10/02)
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- Stereoselective Alkylation of Dianions derived from Chiral Half-Esters of Monosubstituted Malonic Acids: Asymmetric Synthesis of α-Alkyl α-Amino Acids and Key Synthetic Intermediates for Hunteria and Aspidosperma Indole Alkaloids
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Substitution of the chiral half-esters of monosubstituted malonic acids with halides leads to the formations of mixtures of the diastereomeric alkyl- or benzyl-malonic half-esters.The (R)-isomers (13A and 15A-22A) were obtained from the phenylmenthyl half-ester 14 of methylmalonic acid in high diastereoisomeric excess.The same stereoisomers were also produced by reaction of the half-esters 9, 23 and 24 with methyl iodide.Their absolute configurations were determined by transforming the major products into the known α-alkyl α-amino acid derivatives 30, 33 and 35.The major product 43, prepared by allylation of the half-ester 9, was converted into two lactones 41 and 42, key intermediates for synthesis of indole alkaloids of the Hunteria and Aspidosperma types.The mechanism of the above alkylation is discussed.
- Ihara, Masataka,Takahashi, Masanobu,Taniguchi, Nobuaki,Yasui, Ken,Niitsuma, Hiroko,Fukumoto, Keiichiro
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p. 525 - 535
(2007/10/02)
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- REACTIONS OF SCHIFF BASE ANIONS WITH ELECTROPHILES: ROLE OF THE INITIAL STEREOCHEMISTRY
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It is shown that the reactivity towards electrophiles of diastereomeric Schiff bases of *R and *S valine, leucine, phenylalanine and norvaline methyl esters with (1S,2S,5S) or (1R,2R,5R) 2-hydroxy 3-pinanone, is highly dependent on the stereochemistry of the starting product.
- El Achqar, Abdelrhani,Roumestant, Marie-Louise,Viallefont, Philippe
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p. 2441 - 2444
(2007/10/02)
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- SYNTHESE ASYMETRIQUE D'ACIDES AMINES α-DISUBSTITUES
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α-Disubstituted amino acids are prepared with good optical yields by enantioselective substitution using Schiff bases between α-monosubstituted amino acids and (S,S,S) or (R,R,R)-2-hydroxypinan-3-one as chiral reagent.The configuration of these acids is found to be dependent on the shielding effect of their aliphatic chain in the intermediary Schiff dianion.
- Bajgrowicz, J. A.,Cossec, B.,Pigiere, Ch.,Jacquier, R.,Viallefont, Ph.
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p. 3721 - 3724
(2007/10/02)
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