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The mechanism of indazole formation by the polyphosphoric acid catalysed cyclisation of m- and p-nitrophenylhydrazones

✍ Scribed by B. Robinson

Publisher: Elsevier Science
Year: 1967
Tongue: French
Weight: 181 KB
Volume: 8
Category: Article
ISSN: 0040-4039
DOI: 10.1016/s0040-4039(01)89920-2

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✦ Synopsis

Indazoles are formed (1,2,3) when the p-nitrophenylhydrazones of several acetophenones (1,2), benzaldehydes (21, beneophenones (2) and acetylated aromatic hydrocarbons (3) are treated with polyphosphoric acid (PPA) at an elevated temperature. The cyclisation step of this reaction has been postulated (1,2) to involve, after protonation of N2, nucleophilic attack by the Nl atom of the hydrazone group on the ortho-position of the aromatic ring of the ketonic or aldehydic moiety, as shown in I+II.

However, this

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