Studies in terpenoids — VIII (1): Some observations on (−)-3, 3a, 4, 5, 6, 7-hexahydro-3, 3, 6-trimethyl-2H-indazole and its conversion to (+)--carane

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 LiBEt(3)H 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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Synthesis and Properties of Chiral Pyrazolidines Derived from (+)‐Pulegone

Jakob

Herdtweck

Bach

2010

Chemistry A European J

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Studies in terpenoids — VIII (1): Some observations on (−)-3, 3a, 4, 5, 6, 7-hexahydro-3, 3, 6-trimethyl-2H-indazole and its conversion to (+)--carane

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Synthesis and Properties of Chiral Pyrazolidines Derived from (+)‐Pulegone

Synthesis and Properties of Chiral Pyrazolidines Derived from (+)‐Pulegone

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