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A four component reaction involving the coupling of functionalized aldehydes, amines, acid chlorides, and [pi]- and organometallic nucleophiles has been developed to prepare multifunctional substrates that may be employed in subsequent ring-forming reactions to generate diverse arrays of functionalized heterocyclic scaffolds. Allyl metals, Grignard reagents, silyl ketene acetals, silyl enol ethers, and silyloxy furans have been utilized as the nucleophile in the four component reaction (4CR). The 4CR has been sequenced with intramolecular Heck reactions, Diels-Alder and [3+2] cycloadditions, ring closing metathesis (RCM), and Dieckmann condensations to provide a number of diverse heterocyclic structures. The practical utility of this approach to diversity-oriented synthesis (DOS) was further exemplified by its application to the first total synthesis of the isopavine alkaloid roelactamine, which was completed in only four steps from commercially available materials. The application of this methodology towards the synthesis of the Aspidosperma alkaloids rosicine and pseudotabersonine is also presented. To this end, an imine pentadienylation/double RCM strategy has been adopted to rapidly access the pentacyclic core of the aspidospermine alkaloids. This sequence involved the use of a pentadienyl aluminum reagent, which was found to react with aryl imines to give branched products in good yields. / text

All Strychnos and Aspidosperma alkaloids possess a core pyrrolo[2,3-d]carbazole ABCE tetracycle. In order to develop an efficient and divergent methodology for the synthesis of Strychnos alkaloids, a streamlined synthetic sequence to the ABCE tetracycle has been developed. It features a Mitsunobu activation of an N-hydroxyethyl gramine intermediate and subsequent intramolecular aza-Baylis-Hillman reaction. This method was first applied in the total synthesis of (±)-alstolucine B. Additional key steps in the synthesis included (1) chemoselective intermolecular and intramolecular Michael additions and (2) a Swern indoline oxidation. The second application of this method was in the first total synthesis of (-)-melotenine A, a novel rearranged Aspidosperma alkaloid with potent biological activity. Additional key steps in the synthesis included (1) a Piers annulation of a vinyl iodide and a methyl ketone to prepare the D ring and (2) a site-selective intermolecular vinylogous aldol reaction / Chemistry

Thesis advisor: Amir H. Hoveyda / Chapter 1: Efficient Z-Selective Cross-Metathesis of Secondary Allylic Ethers Efficient Z-selective cross-metathesis of secondary allylic ethers were catalyzed by monoaryloxide monopyrrolide molybdenum complexes. Reactions involving both silyl and benzyl protected ethers were demonstrated, as well as ethers containing alkyl, aryl and alkynyl substituents. Mechanistic studies were performed, and the reactions were applied to the total synthesis of several ene-diyne natural products. Chapter 2. Stereoselective Total Synthesis of Disorazole C1 The stereoselective total synthesis of disorazole C1 is reported. The synthesis was completed in 12 longest linear steps. Our synthesis demonstrates the utility of Z-selective cross-metathesis to form both alkenyl borons and alkenyl halides. Another key transformation was a one-pot Suzuki-dimerization reaction to form a symmetric 30 membered ring in relatively high yield. Chapter 3. Stereoselective Cross-Metathesis to Form Trisubstituted Alkenes Initial studies into the stereoselective formation of trisubstituted olefins through molybdenum catalyzed cross-metathesis have been performed. Our mechanistic understanding of the reaction lead us to focus on the synthesis of alkenyl halides, which can be obtained in up 90% yield and 75:25 E:Z selectivity. Chapter 4: Ring-Closing Metathesis in the Synthesis of Natural Products Development of highly efficient and selective ring-closing metathesis reactions have enabled collaborators to successfully implement routes in total synthesis endeavors. A diastereoselective seven-membered ring-closing metathesis enabled the successful synthesis of (±)-tetrapetalone A methyl-aglycon. An enantioselective ring-closing metathesis to form a six membered ring has provided access to enantioenriched aspidosperma alkaloids. / Thesis (PhD) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.