Selenium-stabilized carbanions and synthetic studies on the marinopyrroles

• Author / Creator

  Fernandopulle, Shimal Chamikara

• The first chapter of this thesis describes the development of a general route for the generation of selenium stabilized carbanions via a method that bypasses acid catalyzed formation of selenoacetals. Aldehydes are first converted into α-hydroxystannanes by nucleophilic addition of Bu3SnLi. The resulting hydroxyl is then converted to the corresponding phenyl selenide by treatment with PhSeCN and Bu3P to give the α-(phenylseleno)stannane. Upon treatment with BuLi, the α-(phenylseleno)stannane undergoes preferential Sn/Li exchange to give a selenium stabilized carbanion. This carbanion is condensed with an aldehyde to give a β-hydroxy selenide, which can be converted into an allylic alcohol upon oxidation and selenoxide fragmentation. The formation of α-(phenylseleno)stannanes has been applied to aldehydes containing straight and branched alkyl chains, aromatic substituents, and acid sensitive functional groups. The selenium stabilized carbanions have been condensed with aldehydes containing straight and branched alkyl chains, aromatic substituents, and α,β-unsaturation. The second chapter describes synthetic studies towards two marine natural products, marinopyrrole A and B. The synthesis began with the preparation of the unprecedented N,C2 linked bispyrrole core through a Paal-Knorr condensation onto the amino group of ethyl 3-aminopyrrole-2-carboxylate. Preparation of the densely halogenated core of the marinopyrroles through selective chlorination of the bispyrrole seems to be impossible and was not pursued. Due to unexpected alterations to the electronic structure of the pyrrole ring in the presence of electron withdrawing substituents, preparation of a fully functionalized top ring was unsuccessful. Blocking the 3' position of the bispyrrole with a removable blocking group was also unsuccessful by an ortho metallation approach. Preparation of the halogenated bispyrrole starting with the fully functionalized bottom pyrrole seems promising after a model intramolecular conjugate displacement reaction had shown that it is possible to mount the precursor to the top pyrrole on top of the bottom pyrrole. Work is in progress to prepare the mountable precursor to the top ring.

• Subjects / Keywords

  • Carbanions
  • Selenium
  • Marinopyrroles

• Graduation date

  Fall 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3494Q

• 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.