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Karl Anker Jørgensen

Organocatalytic [6+4] Cycloadditions via Zwitterionic Intermediates: Chemo-, Regio-, and Stereoselectivities

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DOI

  • Peiyuan Yu, University California Los Angeles
  • ,
  • Cyndi Qixin He, University California Los Angeles
  • ,
  • Adam Simon, University California Los Angeles
  • ,
  • Wei Li, University California Los Angeles
  • ,
  • Rasmus Mose
  • ,
  • Mathias Kirk Thøgersen
  • Karl Anker Jørgensen
  • K. N. Houk, University California Los Angeles

The mechanisms and origins of chemo- and stereoselectivities of the organocatalytic [6+4] cycloaddition between 2-cyclopentenone and tropone have been investigated by a combined computational and experimental study. In the presence of a cinchona alkaloid primary amine catalyst and an acid additive, 2-cyclopentenone forms a cross-dienamine intermediate that subsequently undergoes a stepwise [6+4] cycloaddition reaction via a zwitterionic intermediate. The rate-determining transition state features a strong hydrogen-bonding interaction between the tropone oxygen atom and the protonated quinuclidine directing the reaction course leading to a highly periselective [6+4] cycloaddition. The importance of the strong hydrogen-bonding interaction is also demonstrated by the influence of the concentration of the acid additive on the yields and enantioselectivities of the reaction. The corresponding [4+2] cycloaddition reaction has a much higher energy barrier. The enantioselectivity of the [6+4] cycloaddition originates from different repulsive hydrogen-hydrogen interactions that distinguish the diastereomeric transition states.

Original languageEnglish
JournalJournal of the American Chemical Society
Volume140
Issue42
Pages (from-to)13726-13735
Number of pages10
ISSN0002-7863
DOIs
Publication statusPublished - 24 Oct 2018

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