title: L-Proline/CoCl2-catalyzed highly diastereo- and enantioselective direct aldol reactions.
abstract: 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).
authors.affiliation: Institut für Organische Chemie, Universität Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany.
authors.forename: Ananta
authors.initials: A
authors.lastname: Karmakar
authors.forename: Tapan
authors.initials: T
authors.lastname: Maji
authors.forename: Sebastian
authors.initials: S
authors.lastname: Wittmann
authors.forename: Oliver
authors.initials: O
authors.lastname: Reiser
mesh_terms: D000438:Alcohols / Q000737:chemistry*; D000447:Aldehydes / Q000737:chemistry*; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry; D011392:Proline / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000438:Alcohols; D000447:Aldehydes; D007659:Ketones; D003035:Cobalt; D011392:Proline; C018021:cobaltous chloride