N,O-acetals from pivalaldehyde and amino acids for the α-alkylation with self-reproduction of the center of chirality: enolates of 3-benzoyl-2-(tert-butyl)-1,3-oxazolidin-5-ones

摘要: The sodium salts of (S)-alanine, (S)-phenylalanine, (S)-valine, and (S)-methionine are condensed with pivalaldehyde to imines 5. Cyclization by treatment benzoyl chloride in cold CH2Cl2 gives mainly (4:1 > 99:1) the (2S,4S)-4-alkyl-3-benzoyl-2-(tert-butyl)-1,3-oxazolidin-5-ones (6; cis-configuration) high yields (85–95%). oxazolidinones 6 7 deprotonated lithium diethylamide (LDEA) tetrahydrofuran (THF) alkylated (Mel, benzyl bromide) or hydroxyalkylated (benzaldehyde) 4,4-disubstituted 9 10, respectively, diastereoselectivity (9:1 50:1; relative topicity ul). Hydrolysis three amino acids known configuration optical purity indicates that little if any racemization occurs process.