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.
Enantioselective synthesis of α-sulfenylated ketones and aldehydes via α-thiolation of metalated SAMP/RAMP hydrazones
作者:Dieter Enders、Thomas Schäfer、Wolfgang Mies
DOI:10.1016/s0040-4020(98)00481-5
日期:1998.8
Asymmetric α-sulfenylation of lithiated SAMP/RAMP hydrazones (S)-2 with disulfides afforded α-thiolated hydrazones (S,R)-3 in good yields (48–87%) and high diastereomeric excesses (91–96%). Subsequent oxidative cleavage or acidic hydrolysis of the hydrazones furnished α-thiolated ketones (R)-4a-d with high enantiomeric excesses (87–>96%). α-Sulfenylated aldehydes (R)-8a-d were prepared by a similar reaction
Asymmetric Strecker synthesis by addition of trimethylsilyl cyanide to aldehyde SAMP-hydrazones
作者:Dieter Enders、Michael Moser
DOI:10.1016/j.tetlet.2003.09.098
日期:2003.11.10
The asymmetric 1,2-addition of trimethylsilyl cyanide to aldehyde SAMP-hydrazones in the presence of titanium tetrachloride and diethylether in dichloromethane at −100°C up to room temperature, removal of the chiral auxiliary and acid hydrolysis affords α-amino acids in high enantiomeric excesses (ee=94–97%).
Diastereo- and Enantioselective Synthesis of 4,5,6-Trisubstituted and 6-Monosubstituted Piperidin-2-ones
作者:Dieter Enders、Dominika Bartzen
DOI:10.1002/jlac.199719970610
日期:1997.6
convenient, versatile and highly diastereo- and enantioselectivesynthesis of 4,5,6-trisubstituted piperidin-2-ones 1 in satisfactory overall yields is described. The procedure involves the efficient and highly anti-diastereo- and enantioselective Michael addition of aldehydes to enoates via their lithiated SAMPhydrazones, followed by nucleophilic1,2-addition of organometallic reagents to the CN double