Axially Chiral Amidinium Ions as Inducers of Enantioselectivity in Diels−Alder Reactions
Organic Letters2000Vol. 2(2), pp. 179–181
Citations Over TimeTop 12% of 2000 papers
Abstract
[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.
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