The aglycon of pentalinonside (2), a novel seco-pregnane with cage-like DEF-rings, was synthesized. Polyoxygenated DEF-rings were constructed using a known 14,20(16),21(15)-triol derivative via 5-exo-cyclization for the F-ring annulation, followed by C14-21(15) oxidative cleavage and intramolecular acetalization.