Axially chiral amidinium ions as inducers of enantioselectivity in Diels-Alder reactions
[reaction: see text] Enantioselective catalysis of Diels-Alder reactions is mostly achieved by coordinating the dienophile to relatively strong chiral Lewis acids. Here we report on a novel approach employing the hydrogen-bond-mediated association of dienophiles to chiral host molecules. In a reaction forming the steroid skeleton of norgestrel, chiral amidinium ions induce 5:ent-5 ratios of up to 2.5:1. Improved and simplified amidinium catalysts may become interesting candidates to perform stereoselective transformations.
Schuster
T
Institut fur Organische Chemie der J. W. Goethe-Universitat Frankfurt, Frankfurt am Main, Germany.
Bauch
M
Durner
G
Gobel
MW