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■ Oxidative 1,1’-Coupling of Highly Alkylated 2-Methoxycarbonylazulenes

Ryszard Ostaszewski and Hans-Jürgen Hansen*

*Institute of Organic Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland

Abstract

The oxidation of highly alkylated methyl azulene-2-carboxylates 1b – 1d and a dimethyl azulene-1,2-dicarboxylate 1a with TEMPO (2,2,6,6-tetramethyl-piperidine-1-oxyl) in the presence of Et2O·BF3 ((diethyloxonio)trifluoroborate) in benzene at 5 °C leads in moderate yield to the corresponding 1,1’-biazulene-carboxylates 2a – 2d (Table 1).