Catalysis of a Diels-Alder Reaction by Amidinium Ions |
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Authors: | Schuster Kurz Göbel |
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Institution: | Institut für Organische Chemie der J. W. Goethe-Universit?t Frankfurt, Marie-Curie-Strasse 11, D-60439 Frankfurt am Main, Germany. |
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Abstract: | Amidines and guanidines are important functional groups in molecular recognition and host-guest chemistry. Here it is shown that lipophilic amidinium ions catalyze a cycloaddition reaction representing the key step of the Quinkert-Dane estrone synthesis. Hydrogen-bond-mediated association with the organic cation leads to an electrophilic activation of the dienophile and to enhanced rates of the Diels-Alder reaction. The observed effects are similar to those expected from mild Lewis acids. In competition experiments, amidinium catalysis favors the reaction of the less electron deficient dienophile. |
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