- Asymmetric michael addition of malonates to enones catalyzed by a primary Β-amino acid and its lithium salt
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Highly enantioselective Michael addition of malonates to enones was achieved using a mixed catalyst consisting of a primary Β-amino acid, O-TBDPS (S)-Β-homoserine, and its lithium salt. Various cyclic and acyclic enones were converted into 1,5-ketoesters in high yields (up to 92%) with high enantioselectivity (up to 97% ee) under mild reaction conditions. Details of synthesis of the catalyst, optimization of the reaction conditions for the Michael addition reaction, and a plausible reaction mechanism are described.
- Yoshida, Masanori,Narita, Mao,Hara, Shoji
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experimental part
p. 8513 - 8517
(2011/12/03)
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- Tetrahydro-1,3-oxazin-6-ones as templates for the stereoselective synthesis of β-substituted L-aspartic acids
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Protected (4S)-4-carboxytetrahydro-1,3-oxazin-6-ones have been synthesised either by Baeyer-Villiger reaction on a 4-ketoproline derivative or, more directly, from an aspartate derivative. Two strategies have been used to develop these compounds as chiral templates in the synthesis of β-substituted aspartic acids. In the first, formation of an enaminone using Bredereck's reagent, followed by reaction with a Grignard reagent gave a series of alkylidene derivatives which could be reduced from the less hindered side by heterogeneous catalytic hydrogenation to give cis-oxazinones in a completety stereoselective manner. Alternatively, an alkylation strategy, although trans-selective, gave mixtures of isomers. The oxazinones were converted to β-substituted aspartic acids and to regioselectively protected β-substituted aspartic acids without loss of stereochemistry ar either centre.
- Burtin, Guillaume,Corringer, Pierre-Jean,Young, Douglas W.
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p. 3451 - 3459
(2007/10/03)
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- Stereoselective synthesis of β-substituted aspartic acids via tetrahydro-1,3-oxazin-6-ones
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Oxazinones have been synthesised and used as chiral templates in the synthesis of β-substituted aspartic acids. Use of a Bredereck's reagent/Grignard/hydrogenation strategy gave cis-oxazinones with complete stereoselectivity, whereas an alkylation strategy, although trans-selective, gave mixtures of isomers. The oxazinones could be converted to β-substituted aspartic acids and to regioselectively protected β-substituted aspartic acids without loss of stereochemistry at either centre.
- Burtin, Guillaume,Corringer, Pierre-Jean,Hitchcock, Peter B.,Young, Douglas W.
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p. 4275 - 4278
(2007/10/03)
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- Cleavage of Esters under Nearly Neutral Conditions at High Pressure. Chemo- and Regioselective Hydrolysis in Organic Solvents
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Hydrolysis of esters proceeded at room temperature under high pressure in the presence of iPr2NEt or N-methylmorpholine using CH3CN-H2O (60:1) as the solvent.This very mild procedure enables the smooth hydrolysis of biologically important compounds such as amino esters, aliphatic unsaturated fatty esters, and β-hydroxy esters; no racemization, no isomerization, and no side reactions take place.
- Yamamoto, Yoshinori,Furuta, Toshiaki,Matsuo, Jiro,Kurata, Tetsuro
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p. 5737 - 5738
(2007/10/02)
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- MONO-ESTERIFICATION OF N-PROTECTED DI-ACIDS ASPARTIC AND GLUTAMIC BY CHLOROFORMATE ACTIVATION
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Mono-esters of N-protected di-acids aspartic and glutamic are prepared by a one-pot activation with alkyl chloroformates or isopropenyl chloroformate and an additionnal alcohol.This process involves the intermediate internal anhydride formation.
- Jouin, P.,Castro, B.,Zeggaf, C.,Pantaloni, A.,Senet, J.P,et al
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p. 1665 - 1668
(2007/10/02)
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- SYNTHETIC ENZYMES-4. HIGHLY ENANTIOSELECTIVE EPOXIDATION BY MEANS OF POLYAMINOACIDS IN A TRIPHASE SYSTEM: INFLUENCE OF STRUCTURAL VARIATIONS WITHIN THE CATALYSTS.
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The asymmetric epoxidation of chalcone and other electron-poor olefins in a triphase system (water-organic solvent-polyaminoacid) affords optically active oxiranes.The influence of the molecular structure of catalysts and of their secondary conformation on the enantioselectivity of the reaction has also been examined.
- Colonna, Stefano,Molinari, Henriette,Banfi, Stefano,Julia, Sebastian,Masana, Jaume,Alvarez, Angel
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p. 1635 - 1642
(2007/10/02)
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