Synthesis of Panal Terpenoid Core
Panal is a natural bicyclic cadalane-type sesquiterpenoid with an unusual combination of stereocenters. It was isolated in 1988 as an alleged biosynthetic precursor of luciferin (a light-emitting molecule) in a bioluminescent fungus Panellus stipticus. Herein we present the first approach to the synthesis of the terpenoid skeleton of panal, which includes construction of five stereocenters, one of which is easily epimerizable. The key steps in the synthetic approach presented are high-pressure Diels-Alder reaction disobeying the ‘endo rule’, Barbier reductive allylation, and cyclization of trans-decalin ring via ring-closing metathesis.