Fluorine induced pseudo-anomeric effects in methoxycyclohexanes through electrostatic 1,3-diaxial interactions

Bruno Piscelli, William Sanders, Cihang Yu, Nawaf Al-Maharik, Tomas Lebl, Rodrigo Cormanich, David O'Hagan

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Abstract

We report counter‐intuitive axial preferences in non‐stereochemically biased, selectively fluorinated methoxycyclohexanes. These pseudo‐anomeric effects are apparent when electronegative CF2 groups are placed at the C‐2, C‐4 and C‐6 positions of the cyclohexane ring to render the C‐3/5 axial hydrogen atoms electropositive. The electrostatic interaction between these axial hydrogen atoms and the ‐OMe oxygen is stabilising. The effect is explored using high‐level ab initio and DFT calculations in the framework of NBO, QTAIM and NCI analysis across a range of derivatives, and experimentally (19F{1H}‐NMR at −80 °C) for some illustrative examples. The effect is significant in energy terms for a weak interaction, and illustrates a new stereoelectronic aspect attributed to selective fluorine substitution in organic chemistry.
Original languageEnglish
Pages (from-to)11989-11994
Number of pages7
JournalChemistry - A European Journal
Volume26
Issue number52
Early online date18 Aug 2020
DOIs
Publication statusPublished - 16 Sept 2020

Keywords

  • Organofluorine
  • Anomeric effect
  • Conformational analysis
  • Stereoelectronic effects
  • Computational chemistry

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