The Diazotization of 2-Aminoazulene Derivatives. The Formation of 2-Diazo-2,6-azulenoquinone Derivatives

The Diazotization of 2-amino-6-bromo (or alkoxy)-azulene, with alkoxycarbonyl or cyano groups at the 1 and 3-positions, by sodium nitrite in dioxane–sulfuric acid afforded mainly the corresponding 2-diazo-2,6-azulenoquinone derivatives (2a, 2b, 16). The catalytic hydrogenation of these compounds gave 1,3-disubstituted 6-hydroxyazulenes (4a, 4b, 18), from which 1,3-disubstituted 6-alkoxy- or 6-acetoxy-azulenes were obtained. The diazotization of diethyl 2-amino-6-bromoazulene-1,3-dicarboxylate (1a) in dry benzene with isoamyl nitrite in the presence of hydrogen chloride afforded the 2,6-dichloroazulene derivative (20) and the 5-bromo-2-diazo-2,6-azulenoquinone derivative (21); the latter, accompanied by a bromine addition product (22), was also obtained by the bromination of 2a. The diazotization of diethyl 2-aminoazulene-1,3-dicarboxylate (25) afforded 2a and a deamination product (26). The structure and mechanism of the formation of these diazoazulenoquinones are discussed.