Synthesis and Properties of Chiral Pyrazolidines Derived from (+)‐Pulegone |
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Authors: | Florian Jakob Dipl‐Chem Eberhardt Herdtweck Dr Thorsten Bach Prof Dr |
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Institution: | 1. Lehrstuhl für Organische Chemie 1, Technische Universit?t München, Lichtenbergstrasse 4, 85747 Garching (Germany), Fax: (+49)?89‐289‐13315;2. Lehrstuhl für Anorganische Chemie, Technische Universit?t München, Lichtenbergstrasse 4, 85747 Garching (Germany) |
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Abstract: | Several enantiomerically pure N(2)‐substituted octahydroindazoles were prepared as bicyclic pyrazolidine derivatives of (+)‐pulegone. Condensation of pulegone with hydrazine delivered a hexahydroindazole intermediate, which underwent N(2)‐substitution with various electrophiles (alkyl halides, acyl chlorides, phenyl isocyanate). The resulting N(2)‐substituted hexahydroindazoles could be reduced with LiBEt3H in THF to the target compounds. In addition, a N(2)‐thiobenzoyl and some N(2)‐carbamoyl derivatives as well as a N(1)‐substituted octahydroindazole were synthesized. The compounds showed medium activity as iminium ion catalysts promoting quantitatively the Michael addition of nitroethane to cinnamaldehyde in up to 82 % ee for the resulting syn‐diastereoisomer and 78 % ee for the anti‐diastereoisomer. Unexpectedly, the N(2)‐acyloctahydroindazoles were readily oxidized under aerobic conditions. Moreover, it was shown that an oxidation of methyl phenyl sulfide to the corresponding sulfoxide is promoted by an N(2)‐acyloctahydroindazole in deuterochloroform as solvent. It is proposed that the oxidation of N(2)‐acyloctahydroindazoles proceeds by in situ generation of hydrogen peroxide, which in turn can act as an oxidant. |
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Keywords: | heterocycles Michael addition organocatalysis oxidation terpenoids |
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