Journal
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
Volume 2010, Issue 29, Pages 5696-5704Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejoc.201000913
Keywords
Aldol reactions; Asymmetric catalysis; Organocatalysis; Water chemistry
Categories
Funding
- Italian Ministero dell'Universita e della Ricerca (MIUR)
- University of Palermo
- P. O. R. Sicilia
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Ten 4-acyloxy-L-prolines were screened as catalysts at loadings of 2-0.1 mol-% for the direct asymmetric aldol reaction in water by using variable amounts of water. Among them, a new catalyst, the L-proline carrying a trans-4-(2,2-diphenylacetoxy) group, and a catalyst previously synthesized by us, the L-proline carrying a trans-4-(4-phenylbutanoyloxy) group, were found to be excellent catalysts for the aldol reaction between cyclohexanone or cyclopentanone and substituted benzaldehydes when employed in only 1 and 0.5 mol-%, respectively, at room temperature without additives. For such catalysts, high turnover numbers were obtained, which are among the highest values obtained for enamine organocatalysis. Finally, these catalysts can be synthesized by direct O-acylation from inexpensive molecules and successfully used in scaled-up reactions.
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