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Herstellung enantiomerenreiner cis ‐ oder trans ‐konfigurierter 2‐( tert ‐Butyl)‐3‐methylimidazolidin‐4‐one aus den Aminosäuren ( S )‐Alanin, ( S )‐Phenylalanin, ( R )‐Phenylglycin, ( S )‐Methionin und ( S )‐Valin
Author(s) -
Naef Reto,
Seebach Dieter
Publication year - 1985
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19850680117
Subject(s) - chemistry , racemization , enantiomer , amino acid , reagent , chiral auxiliary , stereochemistry , enantiomeric excess , alkylation , alanine , nuclear magnetic resonance spectroscopy , methionine , organic chemistry , enantioselective synthesis , catalysis , biochemistry
Preparation of the Enantiomerically Pure cis ‐ and trans ‐Configurated 2‐( tert ‐Butyl)‐3‐methylimidazolidin‐4‐ones from the Amino Acids ( S )‐Alanine, ( S )‐Phenylalanine, ( R )‐Phenylglycine, ( S )‐Methionine, and ( S )‐Valine In contrast to α‐hydroxy and α‐mercapto carboxylic acids, simple α‐amino acids do not form acetal‐type derivatives ( 2 , X = NH) with pivalaldehyde. For the generation of amino‐acid‐derived chiral, nonracemic enolates ( cf. 3 ), and hence, for the α‐alkylation of amino acids without racemization and without an external chiral auxiliary, the imidazolidinones 12–14 were prepared diastereoselectively. To this end, the methyl or ethyl esters of amino‐acid hydrochlorides were first converted to N ‐methylamides of amino acids which in turn were condensed with pivalaldehyde to give (neopentylidenamino)amides ( 11 ). These Schiff bases could be cyclized either to trans ‐or to cis ‐imidazolidinones ( 12, 14 and 13 , respectively), which were obtained in enantiomerically pure form after recrystallization. The enantiomeric purities were confirmed by HPLC with chiral stationary phases or by 1 H‐NMR spectroscopy in the presence of chiral shift reagents. The configurations ( cis , trans ) were assigned by NOE measurements on 300‐ or 360‐MHz 1 H‐NMR spectrometers.