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Report on an Unusual Cascade Reaction between Azulenes and 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (=4,5-Dichloro-3,6-dioxocyclohexa-1,4-diene-1,2-dicarbonitrile; DDQ)

✍ Scribed by Rolf Sigrist; Hans-Jürgen Hansen

Publisher
John Wiley and Sons
Year
2010
Tongue
German
Weight
412 KB
Volume
93
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

The oxidation of 1‐(3,8‐dimethylazulen‐1‐yl)alkan‐1‐ones 1 with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (=4,5‐dichloro‐3,6‐dioxocyclohexa‐1,4‐diene‐1,2‐dicarbonitrile; DDQ) in acetone/H~2~O mixtures at room temperature does not only lead to the corresponding azulene‐1‐carboxaldehydes 2 but also, in small amounts, to three further products (Tables 1 and 2). The structures of the additional products 3–5 were solved spectroscopically, and that of 3a also by an X‐ray crystal‐structure analysis (Fig. 1). It is demonstrated that the bis(azulenylmethyl)‐substituted DDQ derivatives 5 yield on methanolysis or hydrolysis precursors, which in a cascade of reactions rearrange under loss of HCl into the pentacyclic compounds 3 (Schemes 4 and 7). The found 1,1′‐[carbonylbis(8‐methylazulene‐3,1‐diyl)]bis[ethanones] 4 are the result of further oxidation of the azulene‐1‐carboxaldehydes 2 to the corresponding azulene‐1‐carboxylic acids (Schemes 9 and 10).

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