Catalytic Enantioselective [2,3]-Rearrangements of Allylic Ammonium Ylides: A Mechanistic and Computational Study

Thomas H. West, Daniel M. Walden, James E. Taylor, Alexander C. Brueckner, Ryne C. Johnston, Paul Ha Yeon Cheong, Guy C. Lloyd-Jones, Andrew D. Smith

Research output: Contribution to journalArticlepeer-review

50 Citations (Scopus)

Abstract

A mechanistic study of the isothiourea-catalyzed enantioselective [2,3]-rearrangement of allylic ammonium ylides is described. Reaction kinetic analyses using 19F NMR and density functional theory computations have elucidated a reaction profile and allowed identification of the catalyst resting state and turnover-rate limiting step. A catalytically relevant catalyst-substrate adduct has been observed, and its constitution elucidated unambiguously by 13C and 15N isotopic labeling. Isotopic entrainment has shown the observed catalyst-substrate adduct to be a genuine intermediate on the productive cycle toward catalysis. The influence of HOBt as an additive upon the reaction, catalyst resting state, and turnover-rate limiting step has been examined. Crossover experiments have probed the reversibility of each of the proposed steps of the catalytic cycle. Computations were also used to elucidate the origins of stereocontrol, with a 1,5-S⋯O interaction and the catalyst stereodirecting group providing transition structure rigidification and enantioselectivity, while preference for cation-π interactions over C-H⋯π is responsible for diastereoselectivity.

Original languageEnglish
Pages (from-to)4366-4375
Number of pages10
JournalJournal of the American Chemical Society
Volume139
Issue number12
Early online date23 Feb 2017
DOIs
Publication statusPublished - 29 Mar 2017

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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