Alkanethioimidoyl radicals: evaluation of Β-scission rates and of cyclization onto S-alkenyl substituents

M Minozzi, D Nanni, John Christopher Walton

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)

Abstract

Thioimidoyl radicals were generated by addition of alkylsulfanyl radicals to alkyl isonitriles and were characterized by electron paramagnetic resonance (EPR) spectroscopy. The beta-scissions of their (CS)-S-.-C bonds were studied by variable-temperature EPR spectroscopy and the fragmentation rate constants and activation energies were calculated. The scission rates depend on the stability of the released alkyl radicals but in any case, at room temperature, the processes were fast. Data collected on similar oxyimidoyls showed that their fragmentations are slightly slower compared to those of analogous thioimidoyls. The scission rates of selenoimidoyls could not be studied by EPR and were evaluated by theoretical calculations. EPR experiments also enabled both beta-scission and 5-exo ring closure rate constants of two S-but-3-enyl-substituted imidoyl radicals to be determined, showing that cyclization prevails only at low temperatures. Density functional theory (DFT) theoretical calculations predicted that the fragmentation process preferentially occurs from the s-cis rotamers (X-C bond) of the imidoyl radicals. Thio- and seleno-imidoyls (but not oxyimidoyls) prefer s-trans conformations so that their fragmentations involve prior rotation about the X-C bond.

Original languageEnglish
Pages (from-to)2056-2069
Number of pages14
JournalThe Journal of Organic Chemistry
Volume69
Issue number6
DOIs
Publication statusPublished - 19 Mar 2004

Keywords

  • ELECTRON-SPIN-RESONANCE
  • ENANTIOSELECTIVE TOTAL-SYNTHESIS
  • ABSOLUTE RATE CONSTANTS
  • ALKYL RADICALS
  • ARYL RADICALS
  • ALPHA-(ARYLSULFANYL)IMIDOYL RADICALS
  • CYCLOPROPYLCARBINYL RADICALS
  • (-)-ALPHA-KAINIC ACID
  • ARYLIMIDOYL RADICALS
  • AROMATIC ANNELATION

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