A concise total synthesis of monoterpenoid indole alkaloid (-)-voacafricine A

A concise total synthesis of novel monoterpenoid indole alkaloid (-)-voacafricine A is described, which proceeded in 14 longest linear steps and 5.2% overall yield. Key transformations comprised of (a) an organocatalytically asymmetric Pictet-Spengler cyclization/lactamization cascade reaction generating the key tetracyclic lactam skeleton; (b) asymmetric α -alkylation of carbonyl group induced by Evans’ chiral auxiliary with excellent diastereoselectivity; (c) a highly efficient one-pot desulfurization/hydrogenation/debenzylation transformation using Raney Ni under hydrogen atmosphere; as well as (d) an intramolecular Vorbürggen reaction constructing the quaternary ammonium motif and the final cagelike skeleton. Novel monoterpenoid indole alkaloid (-)-voacafricine A was synthesized via 14 longest linear steps with 5.2% overall yield.