A Chiral Solvent Effect in Asymmetric Organocatalysis
摘要:
Proline-catalyzed aldol reactions between enolizable ketones and aromatic aldehydes can be carried out in propylene carbonate. When enantiomerically pure propylene carbonate is used, the combination of (R)-proline and (R)-propylene carbonate constitutes a matched pair, while (S)-proline and (R)-propylene carbonate constitutes a mismatched pair.
Amino Acid Catalysed Aldol Reactions in Cyclic Carbonate Solvents
作者:Michael North、Maria Morcillo、Pedro Villuendas
DOI:10.1055/s-0030-1260038
日期:2011.6
Ethylene and propylene carbonates are shown to be alternative polar aprotic solvents for cross-aldol reactions catalysed by the primary amino acids (S)-phenylalanine and (S)-tryptophan. In contrast to the corresponding proline-catalysed reactions, both enantiomers of these naturally occurring, primary amino acids are available at low cost. The optimal catalyst and solvent combination needs to be determined on a substrate by substrate basis.
Cyclic carbonates as sustainable solvents for proline-catalysed aldol reactions
作者:William Clegg、Ross W. Harrington、Michael North、Francesca Pizzato、Pedro Villuendas
DOI:10.1016/j.tetasy.2010.03.051
日期:2010.5
Ethylene and propylene carbonates, which can be prepared from epoxides and carbon dioxide, are effective solvents for the proline-catalysed, 100% atom economical, asymmetric aldol reaction between enolisable and non-enolisable carbonyl compounds. The optimal cyclic carbonate to use for a particular aldol reaction along with the need for water as a cosolvent appear to be determined by the polarities of the various components present in the reaction mixture. Both cyclic and acyclic ketones can be used as the enamine precursor and react best with electron-deficient aldehydes, such as 4-nitrobenzaldehyde and pentafluorobenzaldehyde. Chemical yields of up to 99%, diastereoselectivities of up to 100% and enantioselectivities of up to 99% can be obtained. The relative and/or absolute configuration of three of the aldol products are determined unambiguously by X-ray diffraction. (C) 2010 Elsevier Ltd. All rights reserved.
A Chiral Solvent Effect in Asymmetric Organocatalysis
作者:Michael North、Pedro Villuendas
DOI:10.1021/ol1007313
日期:2010.5.21
Proline-catalyzed aldol reactions between enolizable ketones and aromatic aldehydes can be carried out in propylene carbonate. When enantiomerically pure propylene carbonate is used, the combination of (R)-proline and (R)-propylene carbonate constitutes a matched pair, while (S)-proline and (R)-propylene carbonate constitutes a mismatched pair.