Structure Revision and Synthesis of a Novel Labdane Diterpenoid from <i>Zingiber ottensii</i>

The structure of ottensinin, a recently reported constituent of the medicinal plant Zingiber ottensii, was revised by re-evaluation of available NMR data from α-ylidenebutenolide 1 to γ-pyrone 2, whose rearranged labdane skeleton is unprecedented. Structure 2 was proven by synthesis from (+)-sclareolide (nine steps, 27% overall yield) and was further validated by X-ray diffraction analysis of our synthetic sample. A plausible biosynthesis of 2 is proposed.