Studies directed towards the synthesis of irroratin A and studies directed towards the synthesis of rocaglamide and silvestrol
Studies directed towards the total synthesis of the cytotoxic ent-kaurane diterpene irroratin A were carried out. In a model system it was found that Pummerer cyclization gave a bicyclo[2.2.2]octane whereas activation as an allylsilane gave the desired [3.2.1]- bicycle. In a more functionalized system, the use of a rhodium-catalyzed C-H insertion reaction allowed for ready access to the bicyclo[3.2.1]octan-6-one core structure. Attempts to construct the remainder of irroratin A utilizing this core structure were ultimately unsuccessful. The use of a Nazarov reaction for the diastereoselective synthesis of silvestrol and rocaglamide was also studied. A model compound lacking the 6,8-oxygenation present in the natural products was synthesized and subjected to a variety of Lewis and Brønsted acids; in all cases no Nazarov cyclization was observed, but rather (typically) retro Friedel-Crafts acylation. In an attempt to bias the reaction towards the desired pathway more activated substrates were made; however, cyclization was again unsuccessful.