Studies toward the total synthesis of diterpene antibiotic guanacastepene A: Construction of the hydroazulenic core

[GRAPHICS] As a part of studies aimed toward the total synthesis of biologically important natural product guanacastepene A of contemporary interest, a new and concise route to a fully functionally endowed hydroazulenic core is delineated. The strategy involves the building of the requisite stereochemical features on a endo-tricyclo[5.2.1.0(2,6)]decane matrix and excision of the five-membered ring through a retro-Diels-Alder reaction. Generation of the seven-membered ring to access the hydroazulenic framework was achieved employing ring closure metathesis (RCM) reaction as the key step.