A diastereoselective method of preparing benzofuran-based 4,5-spirocycles via metal catalyzed alkenylation is described. The method can be used to provide compounds containing the benzofuranone-4,5-spirocyclic motif of the phainanoids, a class a natural products having immunosuppressive activity. Synthetic analogs of phainanoids, e.g., compounds that mimic the structure of the “western” part of the structure of the phainanoids and that contain the benzofuranone-4,5-spirocycle are described, as well as their synthetic intermediates, and their methods of synthesis.