The synthesis of fragment 13 was carried out from inexpensive (S)-solketal (ca. $1.1/g, see the SI for details). To affix this subunit onto the established chiral spirocyclic core 12, a stereoselective Cu-mediated conjugate addition was applied. The choice of copper (I) reagent was crucial since switching to other common copper (I) salts, such as CuI, CuCN, and CuBr, showed little to no observable conversion (Table ). The stereochemical outcome in this step is controlled by the intrinsic configuration of the spiro-cycle, wherein the side chain blocked the top face. Direct treatment of the in situ generated enolate with Comins' reagent ensured the correct regiochemical olefin outcome and smoothly delivered vinyl triflate 7 as a single product (6.5-g scale), which possessed all skeletal carbon atoms required for 1 and 2.