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Media type:
E-Article
Title:
Eine neue Synthese von 4,5‐Dihydroxy‐pyrazolen
Contributor:
Kirschke, Klaus;
Schmitz, Ernst
imprint:
Wiley, 1985
Published in:Journal für Praktische Chemie
Language:
English
DOI:
10.1002/prac.19853270106
ISSN:
0021-8383
Origination:
Footnote:
Description:
<jats:p><jats:bold>A New Synthesis of 4,5‐Dihydroxy‐pyrazoles</jats:bold></jats:p><jats:p>1‐Aryl‐pyrazolin‐5‐ones <jats:bold>1</jats:bold> are converted by Knoevenagel condensation with acetone or by reaction with 2,2‐dimethyl‐1,3‐dioxolane <jats:bold>6</jats:bold> to 1‐aryl‐4‐isopropyliden‐pyrazolin‐5‐ones <jats:bold>2</jats:bold>. The compounds <jats:bold>2</jats:bold> are epoxidized by hydrogen peroxide forming the spiro‐epoxides <jats:bold>3</jats:bold>, which can be cleaved to 4,5‐dihydroxy‐pyrazoles <jats:bold>4</jats:bold> under acidic conditions. 4‐Acetoxy‐5‐hydroxy‐pyrazoles <jats:bold>13</jats:bold> are formed directly, when <jats:bold>3</jats:bold> are cleaved in presence of acetic anhydride. The 3,3′,3′‐trimethyl‐1‐(4‐nitro‐phenyl)‐pyrazolin‐4‐spiro‐2′‐oxiran‐5‐one <jats:bold>3b</jats:bold> undergoes rearrangement to the 1,3‐dioxolo[4,5‐c]pyrazole <jats:bold>12</jats:bold>.</jats:p>