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

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 simp...

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Bibliographic Details
Published in:Tetrahedron 1998-08, Vol.54 (33), p.9747-9764
Main Authors: Uncuta, Cornelia, Cǎproiu, Miron Teodor, Câmpeanu, Valentin, Petride, Aurica, Dǎnilǎ, Mariana G, Plǎveti, Marieta, Balaban, Alexandru T
Format: Article
Language:English
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Summary: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. Graphic
ISSN:0040-4020
1464-5416
DOI:10.1016/S0040-4020(98)00530-4