Enantioselective syntheses of beta-amino acids: Part 15. Diastereoselective electrophilic amination of chiral 1-benzoyl-2,3,5,6-tetrahydro-3-methyl-2-(1-methylethyl)pyrimidin-4(1H)-one for the asymmetric syntheses of alpha-substituted alpha,beta-diam

摘要

The chiral compounds (R)- and (S)-1-benzoyl-2,3,5,6-tetrahydro-3-methyl-2-(1-methylethyl)pyrimidin-4(1H)-one ((R)- and (S)-1), derived from (R)- and (S)-asparagine, respectively, were used as convenient starting materials for the preparation of the enantiomerically pure alpha-alkylated (alkyl = Me, Et, Bn) alpha,beta-diamino acids (R)- and (S)-11-13. The chiral lithium enolates of (R)- and (S)-1 were first alkylated, and the resulting diasteroisomeric products 5-7 were aminated with 'di(tert-butyl) azodicarboxylate' (DBAD), giving rise to the diastereoisomerically pure (greater than or equal to 98%) compounds 8-10. The target compounds (R)- and (S)-11-13 could then be obtained in good yields and high purities by a hydrolysis/hydrogenolysis/hydrolysis sequence.