摘要:
A short and efficient asymmetric synthesis of beta-substituted gamma-lactams is described. Key steps are the alpha-alkylation of aldehyde SAMP-hydrazones with alkyl bromoacetates, their MMPP mediated conversion to the corresponding nitriles and a reductive cyclization with Raney Ni or Ni boride to the title pyrrolidin-2-ones. The P-substituted gamma-lactams are obtained in three steps, good overall yields (27-78%) and excellent enantiomeric excesses (ee = 93-99%). The applicability of this procedure for the asymmetric synthesis of GABAs (gamma-aminobutyric acids) is demonstrated for (R)-(-)-baclofen hydrochloride, which is obtained in 4 steps, 55% yield and 94% ee.