Synthetic Studies Towards The Total Synthesis Of Cyanthiwigin And Hamigeran Type Natural Products

This dissertation mainly focuses on the synthetic studies of two kinds of terpenoids, which includes the following two parts.The first part is the total synthesis of cyanthiwigin diterpenoids. We developed a flexible route to prepare variety of cyanthiwigins with different structures. In the course of its implementation, the5-6ring system was constructed via an intermolecular formal [4+2] cyclization. After decarboxylation of the benzyl ester with Raney nickel, A-B ring was furnished. Two alkenyl side chains were induced through stereospecific Michael addition and alkylation. C ring was then closed by a ring-closing metathesis, which gave the core tricyclic skeleton (8steps,21%). After regulating the oxidation state of the tricyclic framework, we accomplished the total synthesis of cyanthiwigin A (16steps,4.5%), C (17steps,3.8%), G (15steps,5.7%) and H (17steps,3.5%). We also explored the synthesis of cyanthiwigin B and F, but didn’t achieve ideal results.The second part is the synthetic studies of hamigeran type natural products. We proposed our first generation synthetic route, which was based on the asymmetric Michael addition and Mn (III) promoted radical cyclization. In the course of its implementation, the Michael addition proceeds smoothly with good diastereoselectivity. However, the subsequent Mn (III) promoted radical cyclization proved to be difficult. Then, we planned to develop a general strategy to synthesis hamigerans through a convergent approach. In the course of its implementation, the cyclopentanone fragment, containing a quaternary carbon center, was constructed by means of a AlEt3-promoted tandem reductive rearrangement of1-benzyloxy-2,3-epo-xide. The cross coupling of two fragments was achieved under the standard condition of Suzuki reaction. After an extensive survey of the reaction conditions, we found that the tetra-substituted double bond was inert during the hydrogenation. Alternatively, tricyclic skeleton of hamigeran B could be realized by an intramolecular McMurry coupling from dialdehyde. This part work laid the foundation for the synthesis of related natural products.