Synthesis and Configuration of Natural Dracaenones.

Several dracaenones were synthesized in enantiopure forms for the first time. The key chiral center at C-7 was installed with well-defined stereochemistry using either an Evans aldol condensation or a chiral oxidant-mediated asymmetric epoxidation, while and the critical oxidative coupling was achieved under the PIFA/PTA conditions. Comparison of optical rotations for the synthetic and natural samples allowed for unequivocal assignment of the absolute configurations of the natural dracaenones.