Asymmetric synthesis of β-substituted γ-lactams employing the samp-/ramp-hydrazone methodology. Application to the synthesis of (R-(-)-baclofen
A short and efficient asymmetric synthesis of β-substituted γ-lactams is described. Key steps are the α-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 β-substituted γ-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 (γ-aminobutyric acids) is demonstrated for (R-(-)-baclofen hydrochloride, which is obtained in 4 steps 55% yield and 94% ee.
Enders, Dieter,Niemier, Oliver
p. 385 - 403
(2007/10/03)
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