Total Syntheses of Asperchalasines A-E.

The first total syntheses of asperchalasines A-E, a collection of unprecedented merocytochalasans, are reported. Aspochalasin B, a key tricyclic cytochalasan monomer, was first synthesized through a unified approach that hinges on a Diels-Alder reaction and a ring-closing metathesis reaction. The bioinspired Diels-Alder reactions of aspochalasin B with different epicoccine precursors were then explored, which enabled the divergent access of the heterodimers asperchalasines B-E as well as related congeners. Furthermore, the heterotrimer asperchalasine A was obtained from one epicoccine unit and two aspochalasin B units through a biomimetic Diels-Alder reaction followed by an oxidative [5+2]-cycloaddition.