Elsevier

Tetrahedron

Volume 54, Issue 33, 13 August 1998, Pages 9747-9764
Tetrahedron

Reaction of pyrylium salts with nucleophiles. Part 25. Formation of pyridine-1-oxides, 2-isoxazolines and 1-pyrazoline-1-oxides

Dedicated to the 70th anniversary of Alan Katritzky who, for 35 years, provided us with moral assistance and encouragement.
https://doi.org/10.1016/S0040-4020(98)00530-4Get rights and content

Abstract

The reaction of tri- and tetrasubstituted pyrylium salts with hydroxylamine affords acyclic keto-ketoximes (to be described in a separate paper) which cyclize yielding pyridine-1-oxides and/or 2-isoxazolines. Both these classes of compounds, with many possible applications, can thus be obtained simply and in good yield. The regioselectivity of 2-isoxazoline formation from unsymetrically substituted pyrylium salts is discussed. An unprecedented minor product formed from 2,6-di-t-butyl-4-methylpyrylium perchlorate and two molecules of hydroxylamine is the corresponding 1-pyrazoline-1-oxide. Mechanistic rationalization of all products are provided.

References (34)

  • A.T. Balaban

    Tetrahedron

    (1968)
    A.T. Balaban

    Tetrahedron

    (1970)
  • P.L. Kumler et al.

    Acta Chim. Scand.

    (1968)
  • G. Hawkes et al.

    J. Org. Chem.

    (1974)
  • D.E. McGreer et al.

    Can. J. Chem.

    (1971)
  • E. Schmitz

    Chem. Ber.

    (1958)
  • A.T. Balaban et al.

    Liebigs Ann. Chem.

    (1959)
  • A.T. Balaban et al.

    Pyrylium Salts. Syntheses, Reactions and Physical Properties

  • H. Weber et al.

    Naturforsch.

    (1990)
  • R.F. Evans et al.

    Rec. Trav. Chim. Pays-Bas

    (1959)
  • C.L. Pedersen et al.

    Acta Chem. Scand.

    (1970)
  • K. Dimroth et al.

    Angew. Chem.

    (1968)
  • A.R. Katritzky et al.

    Chemistry of the Heterocyclic N-oxides

  • T. Sasaki et al.

    Tetrahedron

    (1969)
  • R.E. Gawley

    Organic Reactions

    (1988)
  • G.J. Karabatsos et al.

    J. Am. Chem. Soc.

    (1962)
  • A.G. Anderson et al.

    J. Org. Chem.

    (1976)
    A.T. Balaban
  • Cited by (18)

    • Vibrational and electronic circular dichroism studies on the axially chiral pyridine-N-oxide: trans-2,6-di-ortho-tolyl-3,4,5-trimethylpyridine-N-oxide

      2015, Tetrahedron Asymmetry
      Citation Excerpt :

      The pyridine-N-oxide moiety together with the two aryl chromophores have different arrangements in the (aS,aS) and (aR,aR) enantiomers, which allows them to be distinguished by VCD and ECD. The synthesis of pyridine-N-oxide 1 was based on the reaction of pyrylium salts with hydroxylamine40 and is shown in Scheme 1. Dehydration of 3-methyl-pentan-3-ol afforded alkenes 3 and 4.

    View all citing articles on Scopus

    Balaban A. T.; Cravey M.; Ghivirigǎ I. Heterocyclic Commun. 1994, 1, 17, part 24.

    View full text