Theses and Dissertations at Montana State University (MSU)
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Item Expanding the scope of allylbis(silane)-imine cyclizations : a concise approach to the synthesis of the azatricyclic core of Stemofoline and Asparagamine A(Montana State University - Bozeman, College of Letters & Science, 2015) Anderson, Bryon Keith; Chairperson, Graduate Committee: Thomas S. LivinghouseThe Mannich cyclization has been utilized for the synthesis of a number of heterocyclic compounds since its discovery. In this dissertation, a silane-based variant of the Mannich cyclization is discussed. This Mannich-like cyclization has proven to be a powerful tool in governing regio- and stereo- control in carbon-carbon bond forming reactions, which benefit from enhanced nucleophilicity of the C=C pi bond derived from the hyperconjugative effect of the adjacent silicon group. Despite the synthetic utility associated with this transformation, there are comparatively few examples that have explored the intramolecular variant containing silane-based nucleophiles. The utility of a 2-propylidene-1,3-bis(silane) nucleophile in synthesis has also received little attention and it is the goal of this project to further develop this concept, and to apply these findings toward the construction of the azatricyclic core found in the stemona alkaloids Asparagamine A and Stemofoline. The use of a 2-propylidene-1,3-bis(silane) nucleophile in N-acyliminium ion chemistry has been successfully applied towards the construction of the azatricyclodecane cores by employing two cationic desilylative cyclization events. Construction of the requisite nucleophile was accomplished in quantitative yield through a Negishi coupling which employed ZnCl 2 x (THF) 2 and 7 mol% PdCl 2(PPh 3) 2. Within this linear synthesis the enantiopure cores were acquired in 16% (36) and 12% (38) overall yield (16 and 17 steps respectively) from 1,1-dibromo-4-amino-1-butene (18).Item Studies of nucleophile ring opening of oxabicyclic systems in highly polar media : application to a total synthesis of antitumor agent, (-)-epothilone B(Montana State University - Bozeman, College of Letters & Science, 2006) Diep, Nhut Kiet; Chairperson, Graduate Committee: Paul GriecoPolyketides constitute an important family of natural products, having a broad spectrum of biological activity such as antitumor, antibiotic, antifungal, or immunomodulatory action.¹ Many of these compounds possess polypropionates (units with alternating hydroxyl and methyl groups), reflecting their common biosynthesis that is found within nature. Their structural complexity and importance of these compounds as therapeutical agents have made them attractive targets for synthetic organic chemists.¹ Excellent chiral propionate reagents have been developed over the years, including many chiral auxiliaries to direct and promote stereoselectivity, but most recent, investigations have focused upon developing metal-catalyzed asymmetric ring opening. To achieve these results, transition metals (Ni, Pd, Pt) have been employed leading to synthetically useful transformations.