Advances towards Highly Active and Stereoselective Simple and Cheap Proline-Based Organocatalysts

作者：Giacalone Francesco; Gruttadauria Michelangelo^*; Agrigento Paola; Lo Meo Paolo; Noto Renato

来源：European Journal of Organic Chemistry, 2010, (29): 5696-5704.

DOI：10.1002/ejoc.201000913

• Aldol reactions
• Asymmetric catalysis
• Organocatalysis
• Water chemistry

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.

• 出版日期2010-10