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

Article abstract of DOI:10.1002/hlca.19850680521

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