Enantioselective Synthesis of Furo[2,3-<i>b</i>]furans, a Spongiane Diterpenoid Substructure

A short and enantioselective synthesis of cis-fused 5-oxofuro[2,3-b]furans, being found in many spongiane diterpenoid natural products, is reported starting from inexpensive methyl 2-furoate. Moreover, the acid-catalyzed rearrangement of the furo[2,3-b]furan framework A to B is observed for some derivatives, suggesting a simple connection between natural products differing in the absolute configuration of the 3a,6a ring junction.