Studies Towards The Total Synthesis Of Prenylflavonoid Diels-alder Natural Products & Rearranged-abietane Diterpenoid Natural Products

Since the initial studies by Nomura and co-workers in 1980 s, approximately 40 different kinds of structurally unique prenylflavonoid Diels-Alder natural products have been isolated and characterized from various Moraceous plants,which exhibit many promising biological activities including anticancer, anti-HIV, and anti-inflammatory activities. Structurally, these molecules all possess at least one 2’-hydroxychalcone moiety as well as polyphenol structures. Given their striking chemical structures and biological activities, prenylflavonoid Diels-Alder natural products have attracted continuing attention from the synthetic community. This thesis describes the enantioselective biomimetic total syntheses of four important prenylflavonoid Diels-Alder natural products based on a concise and efficient synthetic strategy as the first part. The second part of this thesis focuses on studies toward total syntheses of rearranged-abietane diterpenoid natural products, which contains a common 6/6/6/5-tretracyclic core skeleton.In Chapter 1, we described the isolation,the category and biosynthesis of prenylflavonoid Diels-Alder natural products, along with an overview of Diels-Alderase. We also summarized the previous synthetic works on these natural products.In Chapter 2, we described the concise and efficient enantioselective total syntheses of prenylflavonoid Diels-Alder natural products(-)-kuwanon I,(?)-kuwanon J,(-)-brosimone A and(-)-brosimone B from a common intermediate. Key elements of the synthesis include a biosynthesis-inspired asymmetric Diels-Alder cycloaddition mediated by a chiral VANOL-boron Lewis acid, as well as a process involving regioselective Schenck ene reaction, reduction and dehydration to realize a biomimetic dehydrogenation for generation of the required diene precursor. Furthermore, a remarkable tandem inter-/intramolecular asymmetric Diels-Alder cycloaddition process was applied for the synthesis of brosimone A.In Chapter 3, we described the isolation,the category and biological activity of rearranged-abietane diterpenoid natural products. We explore three different strategies to synthesis of the 6/6/6/5-tretracyclic core skeleton of these natural products.In Chapter 4, the experimental procedure and spectra data of intermediates and products were also recorded in detail.