- Synthesis of pipecolic acid and baikiain
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A straightforward synthesis of pipecolic acid and baikiain was achieved from trans-(2S,4R)-4-hydroxyproline via the key steps of regioselective Baeyer-Villiger reaction. and ring-closing metathesis.
- Chang, Meng-Yang,Kung, Yung-Hua,Wu, Tsun-Chang
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p. 2365 - 2373
(2007/10/03)
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- Ring-closing metathesis of allylic O,O- and N,O-acetals
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A variety of allylic O,O- and N,O-acetals were synthesized using a mild palladium-catalyzed coupling of an alcohol or sulfonamide with an alkyl or aryl 1,2-propadienyl ether. The resulting linear acetals were used for the synthesis of unsaturated rings via ring-closing metathesis, in which the acetal carbon-a precursor for oxycarbenium or N-sulfonyliminium ions, respectively-served as a reactive center for further introduction of functional groups. The products-unsaturated oxygen and nitrogen heterocyclic scaffolds - offer multiple opportunities for derivatization as illustrated with the synthesis of substituted dihydropyrans, chromenes, enantiopure tetrahydropyridines and an enantiomerically pure quinolizidine amino acid.
- Kinderman, Sape S.,Doodeman, Robin,Van Beijma, Jetze W.,Russcher, Jaap C.,Tjen, Kim C. M. F.,Kooistra, T. Martijn,Mohaselzadeh, Homayun,Van Maarseveen, Jan H.,Hiemstra, Henk,Schoemaker, Hans E.,Rutjes, Floris P. J. T.
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p. 736 - 748
(2007/10/03)
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- 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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- A ring-closing metathesis-mediated route to novel enantiopure conformationally restricted cyclic amino acids
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A combination of palladium-catalysed N,O-acetal formation, ruthenium- catalysed ring-closing metathesis and N-sulfonyliminium ion-mediated C-C bond formation constitutes an efficient and versatile route to a set of enantiomerically pure 2,6-disubstituted unsaturated pipecolic acid derivatives.
- Tjen, Kim C. M. F.,Kinderman, Sape S.,Schoemaker, Hans E.,Hiemstra, Henk,Rutjes, Floris P. J. T.
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p. 699 - 700
(2007/10/03)
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- Asymmetric synthesis of cyclic α-amino acids (-)-baikiain and (-)-4 methyleneproline from (S)-Boc-BMI
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The enantiomerically pure glycine derivative tert-butyl (S)-2-(tert-butyl)-3-methyl-4-oxo-l-imidazolidinecarboxylate (Boc-BMI) reacts with (Z)-1,4-dichloro-2-butene and 3-chloro-2-(chloromethyl)-1-propene to give the bicyclic intermediates 5 and 6, respectively. These dialkylated systems are hydrolyzed to the corresponding heterocyclic a-amino acids (S)-baikiain (L-4,5-didehydropipecolic acid) and (S)-4-methylene proline which are obtained in 96 and 90% ee, respectively.
- Mazon, Angel,Najera, Carmen
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p. 1855 - 1859
(2007/10/03)
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