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Title
| - Electrocyclic Ring-Opening/π-Allyl Cation Cyclization ReactionSequences Involving gem-Dihalocyclopropanes as Substrates: Application to Syntheses of (±)-, (+)-, and (−)-γ-Lycorane
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Abstract
| - The readily prepared gem-dibromocyclopropanes (±)-13 and (±)-19 each engage in a silver(I)-promoted electrocyclic ring-opening/π-allyl cation cyclization sequence to deliver the hexahydroindole(±)-20, which participates in a Suzuki cross-coupling reaction with arylboronic acid 3 to give thetetracyclic compound (±)-21. Catalytic hydrogenation of this last compound proceeds in a completelystereoselective manner to give the saturated analogue (±)-24, which undergoes Bischler-Napieralskicyclization on reaction with phosphorus oxychloride. The resulting lactam (±)-25 is then reducedwith lithium aluminum hydride to give (±)-γ-lycorane [(±)-1]. By using (−)-menthyl-derivedcarbamates 27 and 28, this chemistry has been extended to the synthesis of the (+)- and(−)-modifications of the title compound.
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