Synthesis of 6-Amino- and 6-Arylazoazulenes via Nucleophilic Aromatic Substitution and Their Reactivity and Properties.

The nucleophilic aromatic substitution (SNAr) reaction of diethyl 6-bromoazulene-1,3-dicarboxylate (1) with a variety of amines afforded the corresponding 6-aminoazulene derivatives 2a-2j in good-to-excellent yields. 6-Aminoazulene derivatives 3a-3f without the 1,3-diethoxycarbonyl functions were obtained by the deesterification of 2a-2f with 100% H3PO4. The reactivity of 6-aminoazulenes toward the bromination, SNAr, and palladium-catalyzed cross-coupling reactions was also clarified. 6-Arylazoazulenes 13a-13c were also prepared via the SNAr reaction of 1 with arylhydrazines, followed by oxidation with Pb(OAc)4 in the presence of N2H4. The structural, optical, and electrochemical properties of the 6-amino- and 6-arylazoazulenes were revealed by single-crystal X-ray structure analysis, UV/vis spectroscopy, voltammetry analysis, spectroelectrochemistry, and theoretical calculations.