Stereoselective Thioconjugation by Photoinduced Thiol-ene Coupling Reactions of Hexo- and Pentopyranosyl d- and l-Glycals at Low-Temperature—Reactivity and Stereoselectivity Study

Viktor Kelemen, Miklós Bege, Dániel Eszenyi, Nóra Debreczeni, Attila Bényei, Tobias Stürzer, Pál Herczegh, Anikó Borbás

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Abstract

A comprehensive optimization and mechanistic study on the photoinduced hydrothiolation of different d- and l- hexo- and pentoglycals with various thiols was performed, at the temperature range of RT to −120 °C. Addition of thiols onto 2-substituted hexoglycals proceeded with complete 1,2-cis-α-stereoselectivity in all cases. Hydrothiolation of 2-substituted pentoglycals resulted in mixtures of 1,2-cis-α- and -β-thioglycosides of varying ratio depending on the configuration of the reactants. Hydrothiolation of unsubstituted glycals at −80 °C proceeded with excellent yields and, except for galactal, provided the axially C2-S-linked isomers with high selectivity. Cooling was always beneficial to the efficacy, increased the yields and in most cases significantly raised the stereoselectivity. The suggested mechanism explains the different conformational preferences of the intermediate carbon-centered radicals, which is a crucial factor in the stereoselectivity of the reactions.

Original languageEnglish
Pages (from-to)14555-14571
Number of pages17
JournalChemistry - A European Journal
Volume25
Issue number64
DOIs
Publication statusPublished - Nov 18 2019

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Keywords

  • glycal
  • photoactivation
  • stereoselective synthesis
  • thioglycoside
  • thiyl radical addition

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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