Unexpected Beneficial Effect of ortho-Substituents on the (S)-Proline-Catalyzed Asymmetric Aldol Reaction of Acetone with Aromatic Aldehydes
作者:Benjamin List、Alberto Martínez、Manuel van Gemmeren
DOI:10.1055/s-0033-1340920
日期:——
An intriguing effect of electronegative 2,6-substituents on the stereochemical outcome of (S) -proline-catalyzed aldol reactions between benzaldehyde derivatives and acetone is reported. Remarkably high enantioselectivities can be achieved with such substrates.
Highly Enantioselective Organocatalytic Direct Aldol Reaction in an Aqueous Medium
作者:Vishnu Maya、Monika Raj、Vinod K. Singh
DOI:10.1021/ol071013l
日期:2007.6.1
We have demonstrated that small organic molecules 1 and 2 catalyzed the directaldolreaction of both acyclic and cyclic ketones with different aldehydes in an excess of water/brine. Excellent enantioselectivities up to >99% and diastereoselectivities up to 99% with very good yields were obtained by using much lower catalyst loadings (0.5 mol %).
Highly Enantioselective Direct Aldol Reaction Catalyzed by Organic Molecules
作者:Monika Raj、Vishnumaya、Sandeep K. Ginotra、Vinod K. Singh
DOI:10.1021/ol0616081
日期:2006.8.1
compounds catalyzed the directaldolreaction between aldehydes and acetone to provide beta-hydroxy ketones in good yields. The reaction is efficient, and 5-10 mol % of the catalyst and excellent enantioselectivities (97-99% ee) were obtained in both aromatic and aliphatic aldehydes. The presence of a gem-diphenyl group at the beta-carbon is necessary for high enantioselectivity.
Monosalts of N-substituted bimorpholine derivatives are efficient organocatalysts in intramolecular and intermolecular aldol reactions. The properties of the catalysts can be tuned either by the selection of an appropriate acid for the salt formation or by the change of a substituent at the nitrogen atom. In aldolcondensation, i-Pr-substituted bimorpholine is the most stereoselective catalyst affording products