A Computational Study on Lewis Acid Catalyzed Diastereoselective Acyclic Radical Allylation Reactions with Unusual Selectivity Dependence on Temperature and Epimer Precursor

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Abstract

In stereoselective radical reactions, it is accepted that the configuration of the radical precursor has no impact on the levels of stereoinduction, as a prochiral radical intermediate is planar, with two identical faces, independently of its origin. However, Sibi and Rheault (J. Am. Chem. Soc. 2000, 122, 8873-8879) remarkably obtained different selectivities in the trapping of radicals originated from two epimeric bromides, catalyzed by chelating Lewis acids. The selectivity rationalization was made on the basis of different conformational properties of each epimer. However, in this paper we show that the two epimers have similar conformational properties, which implies that the literature proposal is unable to explain the experimental results. We propose an alternative mechanism, in which the final selectivity is dependent on different reaction rates for radical formation from each epimer. By introducing a different perspective of the reaction mechanism, our model also allows the rationalization of different chemical yields obtained from each epimer, a result not rationalized by the previous model. Adaptation to other radical systems, under different reaction conditions, is also possible.
Original languageEnglish
Pages (from-to)11483–11495
JournalJournal of Organic Chemistry
Volume79
Issue number23
DOIs
Publication statusPublished - 5 Dec 2014

Keywords

  • DYNAMIC KINETIC RESOLUTION
  • 2-DIMENSIONAL INFRARED-SPECTROSCOPY
  • ALPHA-HALOACYL IMIDAZOLIDINONES
  • EFFECTIVE CORE POTENTIALS
  • REACTIONS INVOLVING IMINES
  • ELECTRON-RICH OLEFINS
  • NON-RACEMIC STANNANES
  • DIELS-ALDER REACTION
  • AB-INITIO
  • MOLECULAR CALCULATIONS

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