Diethyl 6-amino-2-hydroxyazulene-1,3-dicarboxylate(6a) and 2-acetoxyl derivative (6b) were synthesized by reduction of the 6-azido derivatives (5a,b) with zinc/acetic acid in excellent yields. (5a) and (5b) were prepared by azidation of diethyl 2- acetoxy-6-bromoazulene- 1,3-dicarboxylate. Diazotization of (6a) with sodium nitrite in the presence of concentrated sulfuric acid in dioxane gave diethyl 2-hydroxy-, 2,6-dihydroxy-, and 2- hydroxy-6- [ 2-(2-hydroxyethoxy)ethoxy ] -azulene-1,3- dicarboxylates in 5, 35 and 20% yields, respectively. Similar reaction of (6b) gave the corresponding acetates, compounds of the same type from (6a). No evidence for the formation of 6-diazo-1,3-diethoxycarbonyl-2(6H) azulenone was obtained in the employed reaction conditions.
Journal of the Chinese Chemical Society=中國化學會會誌 41(2), pp.199-203