Asymmetric Synthesis of β-Substituted γ-Lactams Employing the SAMP-/RAMP-Hydrazone Methodology. Application to the Synthesis of (R)-(-)-Baclofen
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.
Asymmetric Synthesis of β-Substituted γ-Lactams Employing the SAMP-/RAMP-Hydrazone Methodology. Application to the Synthesis of (R)-(-)-Baclofen
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.
second intermediate 4 the asymmetric alpha-alkylation of an O-protected derivative of 4-hydroxybutanal was performed exploiting the SAMP/RAMPhydrazone alkylation methodology, and followed by a highly Z-selective Horner-Wadsworth-Emmons reaction under modified conditions. For the synthesis of the polypropionate fragment 5 a diastereoselective syn-aldol reaction was employed between a chiral ethyl ketone
convergent asymmetrictotalsynthesis of pironetin (1), a polyketide with immunosuppressive, antitumor, and plant-growth regulating activities is described. The synthesis was realized by coupling between the C(8)-C(14) 2 and C(7)-C(2) 15 fragments, respectively, by using a Mukaiyama-aldol reaction. The stereogenic centers of each fragment were generated by employing the SAMP/RAMPhydrazone (SAMP=(S)-1-
Reptilian Chemistry: Enantioselective Syntheses of Novel Components from a Crocodile Exocrine Secretion
作者:Zhicai Yang、Athula B. Attygalle、Jerrold Meinwald
DOI:10.1055/s-2000-8229
日期:——
Enantioselective syntheses of the two naturally-occurring diastereomers of dianeackerone (1a and 1b) and of a closely related steroidal β-oxo ester (2), characterized from the paracloacal glandular secretion of the African dwarf crocodile, Osteolaemus tetraspis, are described.
Asymmetric Total Synthesis of (−)-Callystatin A Employing the SAMP/RAMP Hydrazone Alkylation Methodology
作者:Jose L. Vicario、Andreas Job、Michael Wolberg、Michael Müller、Dieter Enders
DOI:10.1021/ol0256116
日期:2002.3.1
[structure: see text] The asymmetrictotalsynthesis of (-)-callystatin A has been achieved. The key steps generating the stereogenic centers rely on the asymmetric alpha-alkylation of aldehydes or ketones exploiting the SAMP/RAMPhydrazone alkylation methodology, as well as an enzymatic enantioselective reduction of a 3,5-dioxocarboxylate. For the construction of the alkene moieties, highly selective
Asymmetric Synthesis of β-Substituted γ-Lactams Employing the SAMP-/RAMP-Hydrazone Methodology. Application to the Synthesis of (R)-(-)-Baclofen
作者:Dieter Enders、Oliver Niemeier
DOI:10.3987/com-05-s(k)41
日期:——
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.