名称:
Enantioselective synthesis of β-amino acids. Part 10: Preparation of novel α,α- and β,β-disubstituted β-amino acids from (S)-asparagine
摘要:
Perhydropyrimidinone (S)-1 is alkylated with very high diastereoselectivity to give trans products (2S,5R)-3, (2S,5R)-4 and (2S,5R)-5. Dialkylation of (S)-1 also proceeds with complete stereoselectivity to afford adducts (2S,5R)-6, (2S,5S)-6, (2S,5R)-7 and (2S,5S)-7. Hydrolysis (6N HCl, 100 degrees C) of monoalkylated derivative (2S,5R)-3 gives enantiopure alpha-substituted beta-amino acid (R)-8. Hydrolysis of dialkylated adducts 6 and 7 affords enantiopure alpha,alpha-disubstituted beta-amino acids (R)- or (S)-9 and (R)- or (S)-10. Related iminoester (2S,6S)-2 is alkylated with complete diastereoselectivity to give products (2S,6S)-11-13 whose hydrolysis under relatively mild conditions (2N CF3CO2H, CH3OH, 100 degrees C) affords enantiopure N-benzoylated beta,beta-disubstituted beta-amino acid esters (S)-14-16, with intact double bonds in the olefinic substituents. (C) 1999 Elsevier Science Ltd. All rights reserved.