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Diastereoselective Hydrogen-Transfer Reactions: An Experimental and DFT Study

Authors

  • François Godin,

    1. Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, H3C 3J7 (Canada)
    2. Bio-organic Chemistry Laboratory, Institut de Recherches Cliniques de Montréal (IRCM), 110 avenue des Pins Ouest, Montréal, Québec, H2W 1R7 (Canada), Fax: (+1) 514-987-5789
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  • Dr. Michel Prévost,

    1. Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, H3C 3J7 (Canada)
    2. Bio-organic Chemistry Laboratory, Institut de Recherches Cliniques de Montréal (IRCM), 110 avenue des Pins Ouest, Montréal, Québec, H2W 1R7 (Canada), Fax: (+1) 514-987-5789
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  • Dr. Serge I. Gorelsky,

    1. Department of Chemistry and Center for Catalysis Research and Innovation, University of Ottawa, 10 Marie Curie, Ottawa, Ontario, K1N 6N5 (Canada)
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  • Dr. Philippe Mochirian,

    1. Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, H3C 3J7 (Canada)
    2. Bio-organic Chemistry Laboratory, Institut de Recherches Cliniques de Montréal (IRCM), 110 avenue des Pins Ouest, Montréal, Québec, H2W 1R7 (Canada), Fax: (+1) 514-987-5789
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  • Maud Nguyen,

    1. Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, H3C 3J7 (Canada)
    2. Bio-organic Chemistry Laboratory, Institut de Recherches Cliniques de Montréal (IRCM), 110 avenue des Pins Ouest, Montréal, Québec, H2W 1R7 (Canada), Fax: (+1) 514-987-5789
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  • Frédérick Viens,

    1. Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, H3C 3J7 (Canada)
    2. Bio-organic Chemistry Laboratory, Institut de Recherches Cliniques de Montréal (IRCM), 110 avenue des Pins Ouest, Montréal, Québec, H2W 1R7 (Canada), Fax: (+1) 514-987-5789
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  • Prof. Dr. Yvan Guindon

    Corresponding author
    1. Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, H3C 3J7 (Canada)
    2. Bio-organic Chemistry Laboratory, Institut de Recherches Cliniques de Montréal (IRCM), 110 avenue des Pins Ouest, Montréal, Québec, H2W 1R7 (Canada), Fax: (+1) 514-987-5789
    • Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, H3C 3J7 (Canada)
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Abstract

Radical reductions of halogenated precursors bearing a heterocycle exo (α) to the carbon-centered radical proceed with enhanced anti-selectivity, a phenomenon that we termed “exocyclic effect”. New experimental data and DFT calculations at the BHandHLYP/TZVP level demonstrate that the origin of the exocyclic effect is linked to the strain energy required for a radical intermediate to reach its reactive conformation at the transition state (ΔEstrain). Furthermore, radical reductions of constrained THP systems indicate that high 2,3-anti inductions are reached only when the radical chain occupies an equatorial orientation. Hydride deliveries to different acyclic substrates and calculations also suggest that the higher anti-selectivities obtained with borinate intermediates are not related to the formation of a complex mimicking an exocycle. From a broader standpoint, this study reveals important conformational factors for reactions taking place at a center vicinal to a heterocycle or an α-alkoxy group.

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