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      Thesis

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      HAGHSHENAS-DISSERTATION-2017.pdf (7.979Mb)
      Date
      2017-10-05
      Author
      Haghshenas, Pouyan 1985-
      ORCID
      0000-0001-5732-4522
      Type
      Thesis
      Degree Level
      Doctoral
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      Abstract
      Enantioenriched amino ketones are convenient building blocks for a variety of synthetic transformations as well as important structural features in a wide array of natural products. N-heterocyclic carbene (NHC) catalyzed benzoin reactions are of great strategic value for obtaining such motifs. Initial efforts focus on a chiral auxiliary approach towards the NHC-catalyzed aza-benzoin transformation. It was investigated whether enantio-enriched α-aminoketones could be obtained using t-butanesulfinimines under NHC-catalyzed reaction conditions. Moderate yields and diastereomeric ratios are obtained between furfural-derived aldehydes and aldimines using this method. The unsatisfactory results prompted further investigation into alternative synthetic methods towards enantioenriched amino ketones. The chemo- and enantioselectivity of cross-benzoin transformations has been the major focus of several recent studies. In contrast, the use of chiral aldehydes in diastereoselective cross- benzoin reactions has received scant attention. This may be explained by the poor reactivity of sterically hindered substrates and/or difficulties in controlling the chemoselectivity. N-Protected α-amino aldehydes, owing to a synergistic balance between their electronic and steric properties, were used to address the chemoselectivity issues associated with NHC-catalyzed cross-benzoin reactions. This thesis describes the first examples of NHC-catalyzed chemo- and diastereoselective cross-benzoin reactions between two aliphatic aldehydes. The optimized reaction conditions can deliver a variety of enantio-enriched α-hydroxy-β-amino ketones with excellent chemoselectivity and good to excellent diastereoselectivity. Having developed viable methodologies to access enantio-enriched amino diols, the application of these methods was investigated in the synthesis of two natural products: D-arabino-phytosphingosine and hyacinthacine A1. Progress towards completion of the synthesis as well as future directions are discussed. With an emphasis on expanding the scope of the application of α-amino aldehydes in NHC-catalyzed transformations, this thesis concludes with a general discussion and proposal for future directions.
      Degree
      Doctor of Philosophy (Ph.D.)
      Department
      Chemistry
      Program
      Chemistry
      Supervisor
      Gravel, Michel
      Committee
      Dimmock, Jonathan R.; Müller, Jens; Pedras, M. Soledade C.; Ward, Dale E.
      Copyright Date
      September 2017
      URI
      http://hdl.handle.net/10388/8167
      Subject
      cross-benzoin reactions
      aza-benzoin reactions
      N-heterocyclic carbenes
      organocatalysis
      D-arabino-phytosphingosine
      hyacinthacine A1
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