I. Lewis acid induced tandem Diels-Alder reaction/rearrangements. II. Total syntheses of natural products using the combined carbon-hydrogen activation/Cope rearrangement as the key step
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The first project of this thesis was the Lewis acid mediated tandem Diels-Alder reaction/rearrangements. There are two novel reactions that have been discovered. One is a Lewis acid induced tandem Diels-Alder reaction/ring expansion as an equivalent of a [4 + 3] cycloaddition. The other is a Lewis acid catalyzed tandem Diels-Alder reaction/retro-Claisen rearrangement, which is an equivalent to an inverse electron demand hetero [4 + 2] cycloaddition. Both reactions are highly diastereoselective and are very useful methodologies to generate bicyclo[3.2.1]oct-6-en-2-ones and 3,4-dihydropyrans, respectively. Moreover, a highly enantioselective formal [4 + 3] cycloaddition has been developed by a tandem asymmetric Diels-Alder reaction/ring expansion. The mechanisms and scopes of both reactions have been studied. The second project was the total syntheses of several natural products using the combined C-H activation/Cope rearrangement as the key step. Eight natural products have been attempted. Six of them have been completed. They are (-)-colombiasin A, (-)-elisapterosin B, (+)-elisabethadione, the (+)- p -benzoquinone 181 , and two unpublished natural products (+)-elisabethadione O -Me ( 236 ) and 237 . The other two compounds are (+)-elisabethamine and (+)-sinulobatin B. Great progress has been made towards the synthesis of (+)-sinulobatin B and this project is still ongoing. The synthesis of (+)-elisabethamine failed and it suggests that this natural product very likely does not exist; at least, it is not stable in the presence of oxygen.