Peroxytungstate anions in asymmetric ion pair catalyzed oxidations

• Main Author: Ye, Xinyi
• Other Authors: Li Tianhu
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Science::Chemistry::Organic chemistry::Oxidation
• Online Access: https://hdl.handle.net/10356/80904; http://hdl.handle.net/10220/48123
• Institution: Nanyang Technological University

The aim of this study is to develop efficient asymmetric ion pair catalysis assisted by metal oxides to realize highly enantioselective oxidation reactions. In this thesis, two projects revealed the novel catalytic system as an excellent strategy in synthetic methodology. In each case, the essence of chemistry was studied mechanistically. The first two chapters introduced the background from two aspects, which included the history of ion pair catalysis (Chapter 1) and application of tungstate salts in oxidation (Chapter 2). The following two chapters presented two projects utilizing the designed strategy. Over the last few years, our group has developed a series of phase-transfer catalysts, which successfully solved problems in the enantioselective addition and substitution reaction under traditional base promoted conditions. Meanwhile, another precedent concept of ion pair catalysis was put forward as a branched subject in this field. Motivated by ion pair concept, the work discussed in this thesis proved the potential of the catalysts developed in our group under a novel working mode. In Chapter 3, bisguanidinium diphosphatobisperoxotungstate BG2+[{PO2(OH)2}2{WO(O2)2}]2- successfully catalyzed asymmetric sulfoxidation, which was applied in synthesis of (S)-Lansoprazole ultimately. The active species was characterized by Raman spectroscopy and supported by computational data. In Chapter 4, according to the success of oxidizing electron poor allylic and homoallylic amines, a further development was established. The real catalyst was a stable compound and demonstrated as bisguanidinium tetraperoxyditungstate BG2+[W2O2(μ-O)(O2)4]2- by single crystal X-ray diffraction. Meanwhile, both experimental and computational data of Raman and IR were collected and compared for analysis and discussion. The perfectly matched spectra show the efficiency of information acquirability via Raman and IR, which has potential application in mechanism exploration in future work of this area.