- 1,5-dimethyl-4-phenylimidazolidin-2-one-derived iminic glycinimides: Useful new reagents for practical asymmetric synthesis of α-amino acids
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New 1,5-dimethyl-4-phenylimidazolidin-2-one-derived acyclic chiral iminic glycine reagents have been prepared and diastereoselectively alkylated with activated alkyl halides and electrophilic olefins in the presence of lithium chloride under (a) strong bases (LHMDS, KOBu(t)) and low temperature (-78 °C,) conditions; (b) solid-liquid phase-transfer catalysis reaction (LiOH, TBAB, -20 °C) conditions, and (c) in the presence of organic bases (DBU, BEMP, TMG, -20 °C). In the case of dielectrophiles C- and N-alkylation takes place to afford heterocyclic derivatives. Hydrolysis of alkylated products has been carried out (a) in two-step procedures with LiOOH or LiOH followed by acidic hydrolysis or Dowex purification, (b) in one single-step under refluxing water to give the corresponding α-amino acid, (c) in the presence of DBU in methanol to provide N-protected α-amino acids methyl esters, or (d) by a protection-hydrolysis procedure to afford N-Boc-protected α-amino acids. The chiral imidazolidinone has generally been recovered in good yield. This methodology has been shown to be useful for the synthesis of acyclic and heterocyclic (S)- and (R)-α-amino acids.
- Guillena,Najera
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p. 7310 - 7322
(2007/10/03)
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- PTC and organic bases-LiCl assisted alkylation of imidazolidinone- glycine iminic derivatives for the asymmetric synthesis of α-amino acids
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Iminic derivatives of (4R,5S)-1,5-dimethyl-4-phenylimidazolidin-2-one and glycine 4 have been highly diastereoselectively alkylated with activated alkyl halides or electrophilic olefins either under PTC conditions or in the presence of the strong organic bases DBU or BEMP at -20°C in the presence of LiCl. Hydrolysis of the alkylated imino imides gave (S)-α-amino acids with recovery of the imidazolidinone chiral auxiliary.
- Guillena, Gabriela,Najera, Carmen
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p. 3935 - 3938
(2007/10/03)
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