Employing an intramolecular Michael addition as a pivotal step, butenolide 5, furans 6 and 7 have been converted to dioxaspiro compounds 8, 9, 10 and 11, whose heterocyclic frameworks constitute important structural units of prehispanolone (2) as well as 14, 15- dihydroprehispanolones (3) and (4), respectively. Hispanolone (1) was converted to 2, 3 and 4 by utilizing a similar strategy.