N-aminopyrroledione-hydrazonoketene-pyrazolium oxide-pyrazolone rearrangements and pyrazolone tautomerism

Ebner, S., Wallfisch, B., Andraos, J., Aitbaev, I., Kiselewsky, M., Bernhardt, P. V., Kollenz, G. and Wentrup, C. (2003) N-aminopyrroledione-hydrazonoketene-pyrazolium oxide-pyrazolone rearrangements and pyrazolone tautomerism. Organic & Biomolecular Chemistry, 1 14: 2550-2555. doi:10.1039/b304070d

Author Ebner, S.
Wallfisch, B.
Andraos, J.
Aitbaev, I.
Kiselewsky, M.
Bernhardt, P. V.
Kollenz, G.
Wentrup, C.
Title N-aminopyrroledione-hydrazonoketene-pyrazolium oxide-pyrazolone rearrangements and pyrazolone tautomerism
Journal name Organic & Biomolecular Chemistry   Check publisher's open access policy
ISSN 1477-0520
Publication date 2003
Sub-type Article (original research)
DOI 10.1039/b304070d
Open Access Status Not Open Access
Volume 1
Issue 14
Start page 2550
End page 2555
Total pages 6
Place of publication Cambridge, United Kingdom
Publisher Royal Society of Chemistry
Collection year 2003
Language eng
Abstract Flash vacuum thermolysis (FVT) of 1-(dimethylamino)pyrrole-2,3-diones 5 causes extrusion of CO with formation of transient hydrazonoketenes 7. The transient ketenes 7 are observable in the form of weak bands at 2130 (7a) or 2115 cm(-1) (7b) in the Ar matrix IR spectra resulting from either FVT or photolysis of either 5 or 1,1- dimethylpyrazolium-5- oxides 8, and these absorptions are in excellent agreement with B3LYP/6-31G* frequency calculations. Under FVT conditions the ketenes 7 cyclize to pyrazolium oxides 8, which undergo 1,4-migration of a methyl group to yield 1,4-dimethyl-3-phenylpyrazole-5(4H)-one 9a and 1,4,4-trimethyl-3-phenylpyrazole-5(4H)-one 9b. All three tautomers of 9a have been characterized, viz. the CH form 9a (most stable form in the gas phase, the solid state and solvents of low polarity), the OH form 9a' (metastable solid at room temperature) and the NH form 9a (stable in aprotic dipolar solvents). The isomeric 1,4-dimethyl-5-phenylpyrazole-3(2H)-one 12 tautomerizes to the 3-hydroxypyrazole 12'. The crystal structure of the hydrochloride 14 of 9a'/9a is reported, representing the first structurally characterised example of a protonated 5-hydroxypyrazole.
Keyword Chemistry, Organic
Density-functional Theory
Wolff Rearrangement
Pyridine Ylide
Q-Index Code C1

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Created: Wed, 15 Aug 2007, 01:34:48 EST