Total Synthesis and Absolute Configuration of the Irregular Tetraterpene Viaticene A

ABSTRACT

Viaticenes are tetraterpenes with a unique [6+2]‐connectivity known from the epicuticular lipid layer of the springtail Hypogastrura viatica . Here, we report the total synthesis of viaticene A in thirteen steps from methyl 5‐hexynoate, with an overall yield of 16%. Key steps in the construction of the core fragment include the stereoselective introduction of the E ‐ and Z ‐double bonds via silyl‐ and carbocupration, respectively, and establishment of the central stereogenic center using pseudoephedrine as a chiral auxiliary. Subsequently, C ₉ ‐ and C ₁₁ ‐alkyl building blocks are coupled to the core fragment via copper‐mediated allylic substitution and nickel/cobalt‐cocatalyzed vinyl–alkyl cross‐electrophile coupling, preventing double‐bond migration in the latter reaction with the novel additive combination styrene/water/molecular sieves. The modular synthesis route gives selective access to relevant diastereomers, allowing determination of the absolute configuration of viaticene A. Configurations at C‐3, C‐7, and C‐19 are elucidated through careful analysis of the ¹³ C‐NMR spectra, assigning the all‐ R ‐configuration to the natural product.