Ringcleavage and reconstruction via intramolecular aldol condensation followed by Grob fragmentation under acetalization conditions (BF3/ethylene glycol) was developed into a novelringcleavage based on intermolecular aldol condensation. On the basis of this reaction, (R,R)-3,5-dimethylcyclohexanone was converted into the chiral straight-chain compound with syndiotactic methyl function. The ring
Highly efficient primary amine organocatalysts for the direct asymmetric aldol reaction in brine
作者:Xiao Ma、Chao-Shan Da、Lei Yi、Ya-Ning Jia、Qi-Peng Guo、Li-Ping Che、Feng-Chun Wu、Jun-Rui Wang、Wei-Ping Li
DOI:10.1016/j.tetasy.2009.05.032
日期:2009.7
amine organocatalysts, derivedfrom natural primary amino acids, in combination with 2,4-dinitrophenol (DNP) have proven to be efficient in the presence of brine without further addition of organic solvents. The system formed by 1f and DNP was the most efficient one; it can catalyze the directaldolreaction with a broad range of ketones and aromatic aldehydes, giving the corresponding aldol products
Organocatalysis with cysteine derivatives: recoverable and cheap chiral catalyst for direct aldol reactions
作者:Shi Li、Xiangkai Fu、Chuanlong Wu
DOI:10.1007/s11164-011-0336-5
日期:2012.1
Highly enantioselective, recoverable and cheap cysteine derivatives have been developed with improved solubility properties in common, nonpolar organic solvents. The reactions were catalyzed using 5 mol% 1e, and the aldol products could be obtained with up to 99:1 syn/anti ratio and >99% ee. The catalyst could be easily recovered and reused, with only a slight decrease of enantioselectivity observed for five cycles. Catalyst 1e can be efficiently used in large-scale reactions with enantioselectivity being maintained at the same level, which offers great possibility for application in industry. (i) Direct aldol reactions proceeded in 1,2-dichloroethane using simple procedures. (ii) Direct S-acylation of cysteine to give organocatalysts 1a–f can be economically carried out easily in a single step from commercially available sources, with both enantiomers being readily available. (iii) 5 mol% catalyst 1e was sufficient to furnish the aldol products in excellent yields (up to 93%) and enantioselectivities (up to 99%). (iv) Catalyst 1e could be easily recovered and reused, and also can be efficiently used in large-scale reactions with enantioselectivity being maintained at the same level, which offers great possibility for applications in industry.
Intramolecular hydrogen bonding guides a cationic amphiphilic organocatalyst to highly stereoselective aldol reactions in water
作者:Ángel M. Valdivielso、Alba Catot、Ignacio Alfonso、Ciril Jimeno
DOI:10.1039/c5ra12135c
日期:——
A novel amphiphilic guanidine organocatalyst, efficient for asymmetric aldol reactions of ketones in water at neutral pH, is disclosed. The reaction presented a clear substrate dependence depicting a free energy linear correlation with ee. Intramolecular hydrogen bonding in the acylguanidine moiety was identified as the key structural motif.
New Simple Hydrophobic Proline Derivatives as Highly Active and Stereoselective Catalysts for the Direct Asymmetric Aldol Reaction in Aqueous Medium
作者:Francesco Giacalone、Michelangelo Gruttadauria、Paolo Lo Meo、Serena Riela、Renato Noto
DOI:10.1002/adsc.200800555
日期:——
different hydrophobic properties of the acyl group were easily synthesized and used as catalysts in the direct asymmetric aldolreaction between cyclic ketones (cyclohexanone and cyclopentanone) and several substituted benzaldehydes. Reactions were carried out using water, this being the best reaction medium examined. Screening of these catalysts showed that compounds bearing the most hydrophobic acyl