Methyl 3-amino-2-methoxy-7-isopropylazulene-1- carboxylate (8a) and its 5-isopropyl isomer (8b) were synthesized by reduction of the 3-nitro derivatives (7a,b) with zinc/acetic acid in excellent yields. 7a and 7b were prepared by nitration and methylation of methyl 7-isopropyl- 2-hydroxyazulene-1-carboxylate and methyl 5-isopropyl-2- hydroxyazulene-1-carboxylate, respectively. Diazotization of 8a with sodium nitrite in trifluoroacetic acid at 0.degree.C gave methyl 5-isopropyl-1,2- azulenequinone-3- carboxylate 9a in 91% yield. Similar reaction of 8b gave the corresponding methyl 7-isopropyl-1,2-azulenequinone-3- carboxylate 9b in 93% yield. No evidence for the formation of 1-diazo-1,2-azulenequinones was obtained.
Journal of the Chinese Chemical Society=中國化學會會誌 43(1), pp.41-44