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Convergent approach to the tetracyclic core of the apparicine class of indole alkaloids via a key intermolecular nitrosoalkene conjugate addition.

Readily available methyl 3-formylindol-2-ylacetate and N-tosyl-4-chloro-3-piperidone oxime have been used to construct the tetracyclic skeleton of the apparicine class of monoterpene indole alkaloids in only four steps in 80% overall yield. Key transformations in this convergent approach involve use of an intermolecular ester enolate/nitrosoalkene conjugate addition to form the C-15/16 bond, followed by a reductive cyclization to construct the C-ring of the tetracycle.