Abstract
The thesis mainly focuses on the photooxygenation of masked o-benzoquinones 100 (MOBs) and its related applications in organic synthesis. Two reaction pathways are discovered. The first one is that singlet oxygen (1O2) reacts on one of electron-rich double bond of MOBs to generate two types of oxidized cyclopentenones 101 and 102 depending on two quenching methods. Its intermediates and the reaction mechanism have also been discussed as well. The second pathway is that endoperoxides 110 were formed through the reaction of 1O2 and electron-rich MOBs. Based on the experimental results, the reaction tendency is affected by the solvent effect, substituent effect and concentration effect (of MOBs). The internal hydrogen bonding provided by the solvents (such as methanol) promotes the formation of cyclopentenones 101 and 102. On the contrary, solvents having no hydrogen bonding ability like chloroform and a high concentration of MOBs make the generation of endoperoxides 110 dominate, especially in the cases of MOBs with R1, R2 = alkyl or OMe and R3 = alkyl groups. Electron-deficient MOBs with R1, R2 = H, R3 = alkyl groups tend to yield cyclopentenones 101 and 102 which have a lot of potential in organic synthesis. (±)-Untenone A was synthesized to demonstrate the efficiency of this methodology. Moreover, hydrolysis followed by decarboxylation of cyclopentenones 101 are of benefit to synthesis of cyclopenteneone-like natural products; the pericyclic reaction of cyclopentenones 102 caused by heat or irradiation 136 also provide an alternative methodology of synthesis of 2-pyrones derivates.