Doctor of Philosophy (PhD)
Recently an efficient methodology, a hetero Pauson-Khand reaction, based on titanium-catalyzed cyclocarbonylation of tethered enals for the general preparation of ¥ã-butyrolactone rings, which are typically embedded in polycyclic systems of many natural products was reported. To demonstrate this new strategy, the total syntheses of the natural products asteriscanolide and ginkgolide were investigated. The first part of this work is dedicated to synthetic efforts toward the total synthesis of asteriscanolide. Approaches highlighted by the [2,3]-Wittig rearrangement, the thermal silyloxy-Cope rearrangement, and a titanium-catalyzed cyclocarbonylation, which is the pivotal step to afford the ¥ã-butyrolactone ring. This study firmly established the utility of cyclocarbonylation methodology for the synthesis of complex, polycyclic organic molecules and demonstrates a useful new approach to the stereocontrolled construction of polycyclic, cyclooctanoid natural products. As part of continuing efforts in applying the cyclocarbonylation strategy towards the total synthesis of natural products, ginkgolides were chosen as second target molecules. The precursor for a hetero Pauson-Khand reaction was efficiently synthesized. It was hoped that the titanium mediated reductive cyclization of the precursor would introduce a butenolide moiety of the target model. Unfortunately, the reductive elimination step was unsuccessful. At this point, further tasks to effect reductive elimination on this system remain, in order to advance towards the target molecule.
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Yang, Jongtae, "Applications of the titanium catalyzed cyclocarbonylation towards natural product syntheses" (2004). LSU Doctoral Dissertations. 2075.