Tetrahydrofuran (THF) and tetrahydropyran (THP) as well as their analogues in higher oxidation states are important structural units found in natural products and bioactive unnatural molecules.[1] Among them, many have all-carbonsubstituted quaternary stereocenters in the 3-/4-(THF) and 3-/5-(THP) positions, such as the highly neurotrophic compounds jiadifenin and tricholomalide A, the anticancer compound maoecrystal V, and ...