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
✍ Scribed by Dieter Seebach; Antoine Fadel
- Publisher
- John Wiley and Sons
- Year
- 1985
- Tongue
- German
- Weight
- 570 KB
- Volume
- 68
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
The sodium salts 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 CH~2~Cl~2~ gives mainly (4:1 to > 99:1) the (2__S__,4__S__)‐4‐alkyl‐3‐benzoyl‐2‐(tert‐butyl)‐1,3‐oxazolidin‐5‐ones (6; cis‐configuration) in high yields (85–95%). The oxazolidinones 6 and 7 are deprotonated with lithium diethylamide (LDEA) in tetrahydrofuran (THF) and alkylated (Mel, 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.