Chemistry, Department of
Department of Chemistry: Dissertations, Theses, and Student Research
ORCID IDs
First Advisor
James M. Takacs
Date of this Version
Summer 7-31-2019
Document Type
Dissertation
Citation
A dissertation presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy
Major: Chemistry
Under the supervision of Professor James M. Takacs
Lincoln, Nebraska, United States, July 2019
COPYRIGHT DISCLAIMER: Parts of the research work compiled in this dissertation are published separately in three academic research journals as listed below; copyright permissions from each were obtained for all:
1. Chakrabarty, S.; Palencia, H.; Morton, M. D.; Carr, R. O.; Takacs, J. M. "Facile access to functionalized chiral secondary benzylic boronic esters via catalytic asymmetric hydroboration", Chem. Sci. (2019) 10: 4,854-4,861. doi: 10.1039/C8SC05613G Copyright © 2019, Royal Society of Chemistry
2. Chakrabarty, S.; Takacs, J. M. "Phosphonate-directed catalytic asymmetric hydroboration: Delivery of boron to the more substituted carbon, leading to chiral tertiary benzylic boronic esters", ACS Catal. (2018) 8: 10,530-10,536. doi: 10.1021/acscatal.8b03591 Copyright © 2018, American Chemical Society
3. Chakrabarty, S.; Takacs, J. M. "Synthesis of chiral tertiary boronic esters: Phosphonate-directed catalytic Asymmetric Hydroboration of Trisubstituted Alkenes", Journal of the American Chemical Society, (2017) 139: 6,066-6,039. doi: 10.1021/jacs.7b02324 Copyright © 2017, American Chemical Society
Copyright for the entirety of the dissertation is reserved by the author. For further permissions related to the materials excerpted, permissions may be sought from the respective journal in which the excerpted portion was published.
Abstract
Over the past 30 years, catalytic asymmetric hydroboration (CAHB) of alkenes has emerged as a leading methodology to access chiral primary and secondary boronic esters. However, it wasn’t until 2015 that directed-CAHB was for the first time shown to efficiently access chiral tertiary boronic esters. The latter are excellent precursors to synthetically challenging structural motifs such as chiral tertiary alcohols, carbinamines and all-carbon quaternary stereocenters via stereospecific C-B bond substitutions. This dissertation focuses on phosphonate-directed CAHB of diverse alkene substrates, including challenging stereodefined trisubstituted alkenes, to efficiently access multifunctional chiral secondary and tertiary boronic esters. Mechanistic insights obtained via deuterium labelling experiments indicate that CAHB reactions proceed via tertiary-alkyl rhodium intermediates for substrates that lead to chiral tertiary boronic esters. The applications of phosphonate-functionalized chiral secondary and tertiary boronic ester products are discussed in the context of stereospecific C-B bond transformations, through phosphonate unmasking methodologies via thiophosphonate and oxophosphonate intermediates, and through synthesis of the cytotoxic natural product bakuchiol.
Advisor: James M. Takacs
Comments
Copyright 2019, Suman Chakrabarty. Used by permission