Unique strategy for the assembly of the carbon skeleton of guanacastepene a using an allenic Pauson-Khand-type reaction

[GRAPHICS] 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.