Total Syntheses of the Cyclobutane-Containing Guaiane-Type Sesquiterpene Daphnepapytone A and Certain Congeners

Daphnepapytone A (1), a structurally unique guaiane-type sesquiterpenoid, has been prepared by total synthesis. So, a (S)-carvone-derived decalindienone was subjected to a photosantonin rearrangement to afford, after additional steps, the natural product oleodaphnone (9). An intramolecular [2 + 2]-cycloaddition of compound 9 followed by an allylic oxidation then gave target 1. Four other structures assigned to guaianes were prepared by related means and so identifying two errors in the recent literature.