3-Benzoyl-2-isopropyl-4-alkyloxazolidin-5-ones as Efficient and Inexpensive Sources of Enantiopure ?,?-Dialkyl ?-Amino Acids and ?,?-Dialkyl ?,?-Diaminopropionic Acids

It is shown that the 3-benzoyl-2-isopropyl-4-alkyloxazolidin-5-ones (12), derived from isobutyraldehyde and ?-amino acids are as efficient as, but more economical than, the corresponding tert-butyl compounds (9), as sources of enantiopure ?,?-dialkylated ?-amino acids (e.g., 21-23). In the absence of alkylating agents, the anions of (2R,4S)-12 and its enantiomer undergo a fragmentation-recombination process to generate (1S,2R,4S)-N-[1-(3-benzoyl- 2-isopropyl-4-methyl-5-oxo-oxazolidin-4-yl)-2-methylpropyl]benzamide ((1S, 2R,4S)-20), and its enantiomer. Acidic methanolysis of these condensation products provides access to ?,?-dialkylated ?,?-diaminopropionic acids [e.g., (2S,3S)-2,3-bisbenzoylamino-2,4-dimethylpentanoic acid methyl ester ((2S,3S)-24)).