Herstellung enantiomerenreiner cis- oder trans-konfigurierter 2-(tert-Butyl)-3-methylimidazolidin-4-one aus den Aminosaeuren (S)-Alanin, (S)-Phenylalanin, (R)-Phenylglycin, (S)-Methionin und (S)-Valin.

Article abstract of DOI:10.1002/hlca.19850680117

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 1H-NMR spectroscopy in the presence of chiral shift reagents.The configurations (cis, trans) were assigned by NOE measurements on 300- or 360-MHz 1H-NMR spectrometers.