A new solution for the construction of the piperidine ring of strychnos alkaloids from 3a-(o-nitrophenyl)hexahydroindol-4-ones. Total syntheses of (±)-tubifolidine, (±)-dihydroakuammicine, and (±)-akuammicine

Alkylation of cis -3a-( o -nitrophenyl)hexahydroindol-4-one 1 with 1-iodo-4-(trimethylsilyl)-2-butyne followed by BF 3 ·Et 2 O-promoted cyclization of the resulting propargylic silane 2 afforded the tricyclic vinylidene ketone 3 , which was further converted to the Strychnos alkaloids tubifolidine, 19,20-dihydroakuammicine, and akuammicine.