Enantioselective synthesis of β-hydroxy-α-amino acid esters by aldol coupling using a chiral quaternary ammonium salt as catalyst

Influence of aromatic substituents on metal(II)salen catalysed, asymmetric synthesis of α-methyl α-amino acids

“…5 Attempts to extend this chemistry to enolates derived from other amino acids, thus allowing the synthesis of a,a-disubstituted amino acids were less successful. 6 Quaternized cinchona alkaloids can also be used to catalyse the alkylation of other enolates, 7 Michael additions, 8,9 aldol reactions, 10 and enone epoxidations. 11 They can also be used in conjunction with achiral palladium complexes to induce the asymmetric allylation of enolates.…”

Straightforward Access to Protected syn α‐Amino‐β‐hydroxy Acid Derivatives

“…For example, syn a-amino-b-hydroxy acids are found in vancomycin [1] or polyoxins [2] (antibiotics), cyclomarins [3] (cytotoxic, anti-inflammatory), ustiloxins [4] (antibiotic, antimitotic), and exochelins [5] (iron chelator). Many studies have been devoted to the synthesis of this unit and most of them rely on an aldol reaction between a glycine equivalent [6] and an aldehyde. Among these glycine equivalents, the most effective are those bearing an isothiocyanate unit as a masked amino group, which proved to be very effective in either diastereoselective or enantioselective aldol reactions.…”

2.07 The Aldol Reaction: Organocatalysis Approach

“…256 This reaction, catalyzed by a cinchonidine-derived ammonium bifluoride 461, gave mostly syn-β-hydroxy-α-amino ester 462 as the major diastereomer with good enantiomeric excess. After 6 years, the Andrus group reported catalyst 465 in the aldol reaction between α-alkoxyacetophenone derivatives 463 and benzaldehyde 464 to give the single syn-product 466 in 76% yield and 80% ee (Scheme 85-2).…”