Investigation of Neglected Areas of Asymmetric Carbonyl Allylboration Chemistry

• Author / Creator

  Bhakta, Urmi Bhusan

• Asymmetric allylboration is a very useful and potent method for the synthesis of chiral homoallylic alcohols, a structural motif present in many natural products and biologically relevant molecules. B/Si double-allylation reagents have also been reported that can lead to chiral homoallylic alcohols with an allylsilane unit. These molecules can then be exploited in the construction of more complex structures. Various total syntheses of important natural products have been achieved exploiting these methods. However, there are a number of areas of allylboration chemistry that have not received much attention. This thesis is aimed towards these areas. Chapter 2 of this thesis is designated for the application of a hydrobenzoin-based chiral synthetic diol (known as vivol)•SnCl4-complex catalyzed allylboration towards the synthesis of chiral homoallylic propargylic alcohols, a structural moiety abundant in natural products. Despite of its importance, there are very few catalytic methods for the synthesis of these compounds and a vivol•SnCl4 asymmetric allylboration methodology has been utilized effectively for this task. Chapter 3 discusses the application of a B/Si double-allylation reagent in imine allylboration to form synthetically useful chiral homoallylic amine. Although B/Si double-allylation reagents have been applied frequently in aldehyde allylation, there is almost no example of imine allylation before this study. Chapter 4 describes the attempted synthesis of a 3-fluoro and 3-trifluoromethyl allylboronate reagent. Had these reagents been prepared successfully, they would have generated chiral α-fluoro and α-trifluoromethyl homoallylic alcohol under vivol•SnCl4-catalyzed allylboration conditions. Despite of the tremendous growth of the field of fluorination and trifluoromethylation chemistry, there is almost no method known towards the synthesis of such building blocks which can be easily manipulated into more useful compounds. Chapter 5 addresses the synthetic attempts towards a stable B/B bidirectional double- allylation reagent, which can afford chiral 1,5-diols present in various natural products. The only known reagent of this kind is an unstable dialkylborane based one, which needs to be prepared and reacted in situ. Having access to a more stable and user-friendly reagent would enable easy synthesis of chiral 1,5-diol building blocks. Future plans regarding these research areas are described in chapter 6.

• Subjects / Keywords

  • Fluorination
  • Asymmetric allylboration
  • Imine allylboration

• Graduation date

  Spring 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3HD45

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.