Diastereoselective intramolecular temporary silicon-tethered rhodium-catalyzed [4+2+2] cycloisomerization reactions: regiospecific incorporation of substituted 1,3-butadienes

Transition metal-catalyzed carbocyclization reactions represent powerful methods for the construction of complex polycyclic systems. We have developed a regiospecific and diastereoselective intramolecular temporary silicon-tethered rhodium-catalyzed 4+2+2] cycloisomerization reaction of a tethered enyne for the construction of tricyclic eight-membered heterocycles and carbocycles. This methodology also allows (E)- and (Z)-olefins to be utilized in a stereospecific manner. The incorporation of either alkene geometry is particularly significant, since related carbocyclization reactions are often limited in this respect. Finally, the ability to utilize carbon-tethered 1,6-enynes and to regiospecifically incorporate substituted 1,3-butadiene derivatives provides exciting opportunities for future applications toward the total synthesis of cyclooctanoid containing diterpenes.