4-endo-Hydroxy-2-oxabicyclo[3.3.0]oct-7-en-3-one as a useful building block in the formal total syntheses of furofurandione natural products

4-endo-Hydroxy-2-oxabicyclo[3.3.0]oct-7-en-3-one (9) is a useful building block in the formal total syntheses of both Types A and B furofurandione natural products. The success of Pd-catalyzed epimerization of the γ-alkenyl substituent of the bislactones makes this methodology useful and versatile.