SILICON-PROMOTED RING CONTRACTIONS IN THE FORMATION OF CARBOCYCLIC SPIRO COMPOUNDS - TOTAL SYNTHESIS OF (-)-SOLAVETIVONE

A new method involving silicon-promoted ring contraction was developed for the synthesis of carbocyclic spiro compounds. In the presence of a Lewis acid, (trimethylsilyl)decalinol 12 and (trimethylsilyl)declain expoide 11 underwent ring contraction in a highly stereoselective manner to afford spiro[4.5]dec-6-enes 14 and 19, respectively. The first total synthesis of optically active solavetivone ((-)-1) was accomplished in 13 steps by use of this new type of reaction as the key step. Utilization of the silicon-promoted ring contraction solves three problems associated with spiro compound synthesis: (1) efficient generation of the quaternary carbon spiro center, (2) full control of the stereoconfiguration of the spiro center during its formation, and (3) stereospecific establishment of chiral centers on both rings of the spiro unit.