First total synthesis of the mastigophorenes C and D and of simplified unnatural analogs

The first total synthesis of the mastigophorenes C (2) and D (3), natural ‘dimeric’ sesquiterpenes isolated from the liverwort Mastigophora diclados with interesting biological activities, is described. As previously for mastigophorenes A (1) and B, the divergent synthetic approach was first optimized on a simplified model system with a tert-butyl group instead of the chiral cyclopentyl residue, also in order to find more easily available compounds with similar or even improved biological activity.