Optimization of ring-contraction of the meso enedione epoxide for chiral building block synthesis

The ring-contraction of the enedione epoxide obtained from the adduct of benzoquinone and cyclopentadiene is mainly affected by the amount of base used. Excellent yields (>80%) of the ring-contracted product were consistently obtained when the epoxide was treated with a 0.5 equiv. of ethanolic sodium hydroxide in ethanol. The versatility of the chiral building block accessible from the ring-contracted product has also been demonstrated by an alternative diastereocontrolled synthesis of (+)-tanikolide, a toxic and antifungal marine natural product isolated from Lyngbya majuscula.