| Fluorenone, tetrahydro-fluorenone and hexahydro-fluorenone containing natural products wildly exist in nature, which have been attracted extensive attentions from organic community because of their novel structures and potential biological activities. This thesis is focused on the development of a series of efficient and mild photo reactions to construct the core structure of hydro-fluorenones which could be used in the total synthesis of corresponding natural products.Part one:We systematically investigated the reaction conditions, scope and application of photo-Nazarov reaction of aryl vinyl ketones to construct hexahydro-fluorenone. This photolytic electrocyclization proceeds in the neutral or basic conditions comparing the conventional acid-catalyzed methods. Photolysis substrates containing various aromatic rings, acid-sensitive groups, cyclohexenyl, cycloheptenyl, and unsaturated pyran with UV-light (254run) smoothly yielded hexahydrofluorenones and related structures. This photo-Nazarov electrocyclization could also be used in the substrates carrying β-alkyl groups on the enone, which gave corresponding polycyclic rings containing quaternary centers. Application of this photo-Nazarov reaction in the synthesis of taiwaniaquinol B and the construction of the core skeleton of asterogynin A were achieved.Part two:A photo induced C-C bond formation to construct tetrahydro-fluorenone was developed. Irradiation of β-halogen (Cl or Br) aryl vinyl ketones with UV-light (254nm) in neutral or basic solution at room temperature gave tetrahydro-fluorenones efficiently. The scope of this photolysis was investigated regarding to the functional-group tolerance; aromatic ring compatibility and cycloalkene ring size. We found that this photolysis provides a mild solution for the preparation of tetrahydro-fluorenones with acid-sensitive functional groups, various (hetero-) aromatic rings. A reasonable process of this photo reaction was proposed based on the mechanism study. |
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