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DOI: 10.1039/A700421D (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 1, 1997, 1799-1804

Preparation and pyrolysis of 1-(pyrazol-5-yl)-1,2,3-triazoles and related compounds[hair space]1

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David Clarke, Richard W. Mares and Hamish McNab

Abstract

1-(Pyrazol-5-yl)-1,2,3-triazoles 8a, 9a and 10 are prepared by cycloaddition of 5-azidopyrazoles with methyl prop-2-ynoate. The regiochemistry of the process is confirmed by synthesis of 9a using an authentic route from ethyl 2-formyl-2-diazoacetate 13. Flash vacuum pyrolysis of 8a, 9a and 10 gives 5-methoxypyrazolo[1,5-a]pyrimidin-7-ones 16–18 by a mechanism involving an unexpected oxoketenimine–imidoyl ketene rearrangement as the key step. The mechanism is supported by a 13C labelling experiment. A general route to pyrazolo[1,5-a]pyrimidin-7-ones from pyrazolylaminomethylene Meldrum's acid derivatives (e.g. 30–32) is also reported.

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