Total Synthesis and Structural Reassignment of (±)-Cereoanhydride

The
first total synthesis of (±)-cereoanhydride has been achieved
under the inspiration of its biosynthetic hypothesis. The tricyclic
skeleton of trypethelone, the proposed biosynthetic precursor of cereoanhydride,
was constructed by an interesting ring expansion of cyclobutenone
in one step in which the introduced acetyl group is pivotal to avoid
the following aerial oxidation. On the basis of X-ray crystallographic
analysis, the structure of cereoanhydride is reassigned to a spiroketal
structure 2, which should be formed through an isomerization
of the originally proposed structure 1.