Tandem Metathesis-Based Natural Product Synthesis & Synthesis of Cyclopropenes and Their Rearrangements

This thesis contains two parts. Part I is about the development and application of tandem metathesis reactions to the synthesis of natural products, which is comprised of first four chapters. Part II is about the synthesis of silylated cyclopropenes and their rearrangement to allenes, which are described in last three chapters, respectively. In the four chapters of Part I, the chapter 1 surveys briefly the recent development in the application of tandem metathesis to natural product synthesis. The chapter 2 depicts total syntheses of four epoxyquinoid natural products by employing enyne metathesis-based tandem reactions as key steps, in which concise total syntheses of (+)-Asperpentyn, (-)-Harveynone, and (-)-Tricholomenyn A were achieved by using a relay metathesis-induced enyne ring-closing metathesis (RCM) and metallotropic [1,3]-shift tandem sequence, and the total synthesis of (+)-Panepophenanthrin was accomplished by using a tandem reaction involving relay metathesis-induced enyne RCM followed by cross-metathesis (CM). The chapter 3 demonstrates a highly diastereoselective ring-rearrangement metathesis (dRRM) of symmetric cyclopentene derivatives to construct the cyclohexene skeletons containing an all-carbon quaternary stereogenic center. And a total synthesis of (±)-nitramine and the synthetic efforts towards galanthamine and caribenol A using this dRRM methodology, are also presented in this chapter. The chapter 4 describes details of the experiments in Part I. In Part II, chapter 5 discloses an unprecedented cyclopropenation reaction involving Cα-Si bond insertion wherein alkylidene carbenes derived from α-silyl ketones selectively insert into more electron-rich Cα–Si bond. Chapter 6 mainly discusses transition metal-catalyzed ring opening of cyclopropenes, including the development of a novel PtCl2-catalyzed rearrangement of silylated cyclopropenes to the corresponding allenes and the preliminary results regarding PtCl2-catalyzed dimerization of 1-alkylcyclopropene 3-carboxylates to trienes. The experiments about Part II are detailed in the chapter 7.