hetero-Diels-Alder Reactions of Masked o-Benzoquinones
| Autor: | Ken-Ching Lin, 林根靖 |
|---|---|
| Rok vydání: | 2002 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 91 The investigations on the hetero Diels-Alder reactions of masked o-benzoquinones (MOBs) and the studies toward the total synthesis of (±)-lycoricidine are described. The thesis consists of four parts: first chapter is concerned with the hetero Diels-Alder reactions of MOBs with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD). The second chapter deals with hetero Diels-Alder reactions of MOBs with nitroso compounds. The third chapter is concerned with hetero Diels-Alder reactions of MOBs with chiral nitroso compounds. The fourth chapter describes the studies toward the total synthesis of (±)-lycoricidine. The hetero Diels-Alder reactions of MOBs generated from the oxidation of 2-methoxyphenols with PTAD are discussed in chapter 1. In most of the cases studied, PTAD reacted efficiently with MOBs at 0 oC. In the second chapter, the hetero Diels-Alder reactions of MOBs with nitroso dienophiles are described. The reactions of nitroso compounds with MOBs bearing both electron-releasing as well as electron-withdrawing groups proceeded with high efficiency in highly regioselective manner and a single cycloadduct was obtained in each case. The theoretical calculations performed at HF/6-31G* level have supported the experimentally observed selectivities. The third chapter deals with the synthesis and asymmetric Diels-Alder reactions of chiral nitroso dienophiles with MOBs. Several nitroso compounds bearing 8-aryl-substituted menthol derivatives were utilized for the asymmetric Diels-Alder reactions with MOBs and diastereomeric excesses up to 90% were obtained. The investigations on the utilization of MOB hetero-Diels-Alder strategy in the studies toward the total synthesis of (±)-lycoricidine are detailed in the last chapter. The commercially available and inexpensive guaiacol was chosen as the starting material. One of the key steps in the retrosynthetic analysis is the coupling between o-bromo benzoyl chloride and a cyclohexene derivative derived from the Diels-Alder reaction of MOB, generated from guaiacol and a nitroso dienophile. After several setbacks, a route comprising of MOM groups protected aminocyclo hexenediol has been followed. The selective reduction of the cycloadduct followed by the protection of free hydroxyl functionality and subsequent cleavage of N-O bond provided aminocyclohexenediol. Up to now, we finished the precursor of the N-acylation. It is expected to reach (±)-lycoricidine from several synthetic operations. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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