Synthetic studies on lycopodine: construction of hexahydrojulolidine core by intramolecular Mannich reaction

The tricyclic core skeleton of lycopodine was constructed by the intramolecular Mannich reaction of a 12-membered cyclic amine. The concise assembly of the macrocyclic intermediate was executed by the sequential inter- and intramolecular N-alkylation of a linear diol using Ns-amide. The fully functionalized diol was prepared via Michael reaction of enone and malonate. The key Mannich reaction proceeded smoothly in the presence of silica gel to provide the tricyclic core skeleton of lycopodine.