Asymmetric syntheses of 1-amino-2-phenyl(alkyl)cyclopropanecarboxylic acids by diastereoselective cyclopropanation of highly functionalized monochiral olefines

Abstract

Monochiral α-benzamidocinnamic esters of N-methylephedrine or mandelic derivatives and benzylidene or alkylidene diketopiperazines, all obtained from oxazolones, react with diazomethane to give moderate to high diastereomeric excesses (d.e.) of pyrazoline derivatives which, after photolysis and acid hydrolysis of the resulting cyclopropyl compounds, gave (1 R, 2 R)-, (1 S, 2 S)-or ( 1S, 2R)-1-amino-2-phenyl(alkyl)cyclopropanecarboxylic acids. The enantiomerically pure dipeptide of the (1 R, 2 R) enantiomer with S-proline was also obtained by selective cleavage of the diketopiperazine moiety. The structure of all compounds has been assessed by NMR studies and y X-ray crystallography and analysis of an intermediate spiroderivative.