University of Hertfordshire

  • Demeter Tzeli
  • Petros G. Tsoungas
  • Ioannis D. Petsalakis
  • Paweł Kozielewicz
  • Mire Zloh
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Original languageEnglish
Number of pages11
Pages (from-to)359-369
JournalTetrahedron
Journal publication date14 Jan 2015
Volume71
Issue2
Early online date13 Nov 2014
DOIs
Publication statusPublished - 14 Jan 2015

Abstract

Oxidatively generated β-nitroso-o-quinone methides undergo an o- and/or peri-intramolecular cyclization to arene-fused 1,2-oxazoles, 1,2-oxazines or indoles. The reaction, found to be an innate process, has been scrutinized by DFT/B3LYP and MP2 calculations. Due to its rapidity, the process has been termed a 'reclusive' one. Competing o-(1,5)- and peri-(1,6)- or (1,5)-cyclizations advance via successive transition states. Activation barriers are drastically lowered in AcOH, probably through H hopping or tunnelling whereas they are barely reduced in other solvents. Aromaticity indices, such as HOMA, IA and ABO, have been used to assess the stability of the end-heterocycles and the preponderance of any one of them. Thus, the preferred cyclization mode, that is, the prevalence or exclusive formation of one of the heterocycles, appears to be oxidant-directed rather than determined by the quinone methide geometry. The question of the peri-cyclization, being a primary or a secondary process, has been tackled.

Notes

Date of Acceptance: 06/11/2014

ID: 7970339