Copper(I)/guanidine catalyzed asymmetric allylic borylation reaction

• Main Author: Ge, Yicen
• Other Authors: Tan Choon Hong
• Format: Theses and Dissertations
• Language: English
• Published: 2018
• Subjects: DRNTU::Science::Chemistry::Organic chemistry
• Online Access: http://hdl.handle.net/10356/73455
• Institution: Nanyang Technological University

Chiral organic boronates are versatile reaction intermediates as they could be readily converted into highly functionalized compounds with high regioselectivity and stereoselectivity. Although numerous reports arised in the enantioselective conjugated borylation and asymmetric hydroboration, limited attention was paid in the area of enantioselective allylic borylation. Additionally, allylboronates could further undergo nucleophilic addition to aldehydes, ketones or imines in which homoallylic alcohols or amines were obtained stereoselectively. However, stereoconvergent synthesis of such enantiopure allylboronates from racemic allylic substrates or the mixture of E/Z isomers, still remained challenging, especially for reactive allylic halides. In the 1st Chapter of this thesis, a brief introduction will be presented involving the properties of organo boron compounds, utilization of diboron reagents, Miyaura borylation reaction and current achievement on allylic borylation as the background of our research. In the following Chapter 2, our exploration on copper/guanidinium catalyzed allylic borylation reactions will be introduced. We managed to explore that in the presence of copper bicyclic guanidinium salt we were able to afford the desired allylic boronate with high enantioselectivity under optimized condition. Upon scope investigation, this novel system was found able to furnish a series of cyclic or linear secondary/tertiary boronates in a stereoconvergent manner. After that, the reaction mechanism was carefully probed with a variety of methods and techniques, including kinetic studies, 1H and 11B NMR, EPR 7 spectroscopy, X-ray crystallography, and radical clock and trapping experiments. With the results noted in Chapter 3, the reaction was proposed to undergo an enantioconvergent SN2’ substitution. Then the scaled-up reaction and further application of enantioenriched allylic boronates were investigated. Finally, the synthetic routes and characterization data are listed in Chapter 4, and the soft copies of original spectra are attached in the Appendix.