Helvetica Chimica Acta p. 1824 - 1840 (1988)
Update date:2022-08-04
Topics: Column chromatography Yield NMR spectroscopy Enantiomeric excess (ee) Deprotonation Nucleophilic substitution HPLC (high-performance liquid chromatography) Protecting group Leaving group Solvent Effects Alkylating Agent Chiral Auxiliary Reaction Optimization Enolate Diastereoselective alkylation Stereocenter Diastereomer Ratio (dr) Phase-Transfer Catalyst (PTC)
Estermann, Heinrich
Seebach, Dieter
The enantiomerically pure 3-aminobutanoic acids (R)- and (S)-6 are readily available by preparative HPLC separation of the two diastereoisomers 5 obtained from addition of (S)-phenethylamine to methyl crotonate and subsequent hydrogenolysis (Scheme 2). (S)-methyl 3-(benzoylamino)butanoate ((S)-3) is also available by enzymatic kinetic resolution with pig-liver esterase.The N-benzoyl- and N-benzyloxycarbonyl derivatives rac-3, 8,and 9 of 3-aminobutanoates are doubly deprotonated with LDA and alkylated or aminated in high selectivity (17 examples, relative topicity like; see Tables 1 and 2).The configuration of three of the products is assigned (Schemes 4-6), and in four cases, the free α-substituted β-amino acid is prepared by acidic hydrolysis (see Table 3).It is shown that the doubly lithiated β-amino-acid derivative is solubilized, and its reactivity may be strongly influenced by the presence of 3 equiv. of LiCl.
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