The Synthesis of Velloziolide via Nicholas Reaction Based γ-Carbonyl Cations

The total synthesis of the 9,11-seco-rosane diterpene velloziolide (1) has been accomplished by employing the Nicholas reaction chemistry of 2a as a gamma-carbonyl cation equivalent. An initial model study demonstrated the utility of Nicholas reactions of 2 in the generation of 4-arylalkynoate-Co(2)(CO)(6) complexes, and in conjunction with Gilman cuprate addition and Johnson-Claisen rearrangement chemistry, the preparation of a 3-methyl-3-vinyl-4-arylalkanoate model for velloziolide. The Nicholas reaction/gamma-carbonyl cation methodology was then employed twice in the total synthesis to incorporate onto 3,4-methylenedioxytoluene the 4-carbon unit that became the gem-dimethyltetralin portion of the velloziolide and, subsequently, to incorporate the gamma-arylalkanoate function of the epsilon-lactone.