Institut für Organische Chemie, Universität Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany.
Chemistry. 2011 Sep 19;17(39):11024-9. doi: 10.1002/chem.201101299.
The CoCl(2)/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 CoCl(2) 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 Co(II).
CoCl(2)/L-脯氨酸（1:2）体系被发现是直接Aldol 反应的优秀催化剂。与使用脯氨酸作为唯一催化剂相比，该催化剂体系具有出色的产率（高达 93%）和显著提高的非对映选择性（高达 45:1）以及对映选择性（高达 99%以上的 ee 值）。该催化剂体系成功应用于环状和非环状酮与芳香族和脂肪族醛的组合。提出了 CoCl(2)和脯氨酸（1:2）的原位螯合通过涉及脯氨酸-烯胺和醛通过螯合到 Co(II)的定位的六元 Zimmerman-Traxler 型过渡态来促进反应。
