Oxidative Ringöffnung von 3(2H)‐Pyrazolonen mit Periodat

Abstract

Im Gegensatz zu den Aminopyrazolonen 1 sind die Pyrazolone 3 und 5 gegen Singulett‐Sauerstoff stabil. Keine Unterschiede zeigen die Titelverbindungen 1, 3 und 5 bei der Reaktion mit Natriummetaperiodat, wobei unter Ringöffnung die Oxidationsprodukte 2, 4 und 6 gebildet werden. Die 1H‐ und 13C‐NMR‐Spektren von 4 zeigen ähnlich wie bei 2 das Vorliegen rotamerer Formen bei Raumtemperatur.

Mild Nitration of Pyrazolin‐5‐ones by a Combination of Fe(NO3)3 and NaNO2: Discovery of a New Readily Available Class of Fungicides, 4‐Nitropyrazolin‐5‐ones

“…[45] In addition, the oxidative destruction of the pyrazolin-5-one ring is also known. [46,47] Among the recent work devoted to the functionalization of pyrazolin-5-ones by the attack of electrophiles [48][49][50][51][52][53][54][55] or radicals [56][57][58] at the 4-position of the heterocycle, only one involved the creation of the CÀN bond, in which azodicarboxylates were used as the nitrogen electrophiles. [52] In this work we proposed aF e(NO 3 ) 3 /NaNO 2 nitrating system that has allowed the synthesis of 4-nitropyrazolin-5-ones bearing as ubstituent at C-4 under ambient conditions (Scheme 1d).…”

“…These processes proceed easily even under the action of molecular oxygen at room temperature . In addition, the oxidative destruction of the pyrazolin‐5‐one ring is also known . Among the recent work devoted to the functionalization of pyrazolin‐5‐ones by the attack of electrophiles or radicals at the 4‐position of the heterocycle, only one involved the creation of the C−N bond, in which azodicarboxylates were used as the nitrogen electrophiles …”