Asymmetric Synthesis of (+)-Galbelgin, (−)-Kadangustin J, (−)-Cyclogalgravin and (−)-Pycnanthulignenes A and B, Three Structurally Distinct Lignan Classes, Using a Common Chiral Precursor

The enantioselective synthesis of three structurally distinct classes of lignan from a single, aza-Claisen-derived, chiral morpholine amide is reported. The class of lignan formed is dependent on the substitution pattern in the aryl rings and choice of protecting group on a key benzylic hydroxyl group. The methodology has been used to asymmetrically synthesize and determine the absolute stereochemistry of lignans (+)-cyclogalgravin 3, (-)-pycnanthulignene A 4, (-)-pycnanthulignene B 5, and (-)-kadangustin J 8.