Asymmetric Total Synthesis of Lancifodilactone G Acetate. 2. Final Phase and Completion of the Total Synthesis

The asymmetric total synthesis of lancifodilactone G acetate was accomplished in 28 steps. The key steps in this synthesis include (i) an asymmetric Diels–Alder reaction for formation of the scaffold of the BC ring; (ii) an intramolecular ring-closing metathesis reaction for the formation of the trisubstituted cyclooctene using a Hoveyda–Grubbs II catalyst; (iii) an intramolecular Pauson–Khand reaction for construction of the sterically congested F ring; (iv) sequential cross-metathesis, hydrogenation, and lactonization reactions for installation of the anomerically stabilized bis-spiro ketal fragment of lancifodilactone G; and (v) a Dieckmann-type condensation reaction for installation of the A ring. The strategy and chemistry developed for the total synthesis will be useful in the synthesis of other natural products and complex molecules.