Synthesis of polycyclic natural products

Pyranonaphthoquinones show characteristic biological activities and have in common the isochromanquinone skeleton. As a consequence of their interesting structures and useful biological activities, new synthetic approaches have been developed. Our generally useful three step (Michael addition, oxidation and reduction) sequence for pyranolactone subunits represents a valuable contribution to synthetic methodology. Efforts toward the synthesis of these natural pyranonaphthoquinones led us to generate a common intermediate by which the more complex pyranonaphthoquinones can be prepared. This extremely convergent approach will permit the direct synthesis of biologically active analogues and may also aid in the structure identification of quinone natural products. In the context of extending our Diels-Alder/retro-Claisen (DARC) strategy to more complex pyranonaphthoquinones such as SCH 38519 and medermycin, a new synthesis of dialdehyde sugars using a Michael addition/aldol condensation sequence has been developed. It is complementary to previously reported methods for the production of C-glycosyl compounds;Studies on the application of functionalized bridgehead radical intermediates in natural products synthesis led us to discover a new pathway to bicyclo(3.3.0) octanes and their 3-aza counterparts by nucleophilic addition/ring contraction of bridgehead bromides. The natural product modhephene was synthesized by use of this rearrangement methodology. A new, highly efficient bridgehead radical approach to the ABDE ring skeleton of lycoctonine-type diterpenoid alkaloids has been developed. The facile carbon-carbon bond formation at the bridgehead makes this process particularly attractive for the synthesis of polycyclic diterpene alkaloid systems