Unique Strategy for the Assembly of the Carbon Skeleton of Guanacastepene A Using an Allenic Pauson−Khand-Type Reaction

[reaction: see text] An approach to the highly functionalized tricyclic core of guanacastepene A has been developed using a rhodium(I)-catalyzed allenic Pauson-Khand reaction. This approach constitutes a conceptually novel strategy for the synthesis of this tricyclic framework, whereby the six-membered ring is formed intially followed by simultaneous formation of the five- and seven-membered rings.