Exploiting multiple nucleophilic sites on pyrrole for the assembly of polyheterocyclic frameworks: application to a formal total synthesis of (±)-aspidospermidine

Abstract

The tricyclic ketone 19, an advanced intermediate in Aubé's recently reported synthesis of aspidospermidine (4), is prepared in twelve steps from pyrrole (3). The key transformations involve a previously described intramolecular Michael addition reaction of pyrrole 10 and intramolecular Friedel–Crafts type cyclisation of the derived carboxylic acid 15 to ketone 16. Careful hydrogenation of this last compound afforded the fully saturated alcohol 17 which was readily oxidised to the target ketone 19.