Thermal rearrangements of tetrahydroimidazo[1,5-b]isoxazole-2,3-dicarboxylates. Synthesis of 3H-imidazol-1-ium ylides and their silver derivatives

Coskun N., Cetin M.

TETRAHEDRON, vol.66, no.11, pp.2053-2060, 2010 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 66 Issue: 11
  • Publication Date: 2010
  • Doi Number: 10.1016/j.tet.2010.01.037
  • Journal Name: TETRAHEDRON
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.2053-2060
  • Keywords: Dipolar cycloaddition, Cyclic nitrones, 4-Isoxazolines, Ylides, Rearrangement, NHCs, Ag(I) metallated imidazolium ylides, IMIDAZOLINE 3-OXIDES, DIASTEREOSELECTIVE ADDITION, 1,3-DIPOLAR CYCLOADDITION, REGIO, REACTIVITY, COMPLEXES
  • Bursa Uludag University Affiliated: Yes

Abstract

Isoxazolines 2 from the cycloaddition of imidazoline 3-oxides 1 with DMAD undergo rearrangement to 3,4-dihydro-2H-imidazol-1-ium-1-(1,2-bis-methoxycarbonyl-2-oxo-ethanides) 3, which spontaneously undergo elimination to give 3H-imidazol-1-ium-1-(1,2-bis-methoxycarbonyl-2-oxo-ethanides) 5 or 1H-imidazoles 6 when heated in toluene at reflux. The presence of the aromatic ring at C-6 decelerated the conversion and enhanced the yield of 5. Solvents more polar than toluene (e.g.. DMSO) provided quantitative conversion of 2 into 6 in mild conditions, while in less polar solvents such as CCl4, the reaction rate was lowered and the yield of 5 enhanced. C-2 unsubstituted ylides 5 were treated with Ag2O or AgNO3 in the presence of Et3N at room temperature to give C-2 metallated derivatives 9 in excellent yields. (C) 2010 Elsevier Ltd. All rights reserved.