L-Proline/CoCl2-Catalyzed Highly Diastereo- and Enantioselective Direct Aldol Reactions
作者:Ananta Karmakar、Tapan Maji、Sebastian Wittmann、Oliver Reiser
DOI:10.1002/chem.201101299
日期:2011.9.19
AbstractThe CoCl2/L‐proline (1:2) system was found to be an excellent catalyst for direct aldol reactions. Excellent yields (up to 93 %) and a significant improvement in diastereoselectivity (anti/syn up to 45:1) as well as enantioselectivity (up to more than 99 % ee) compared with using proline as the sole catalyst were observed. This catalyst system was successfully applied to both cyclic and acyclic ketones in combination with aromatic and aliphatic aldehydes. In situ chelation of CoCl2 and proline (1:2) is proposed to promote the reaction through a six‐membered Zimmermann–Traxler type transition state involving the positioning of proline‐enamine and the aldehyde through chelation to CoII.