2-Amino-6-bromoazulene derivatives reacted with cyclic amines (pyrrolidine, piperidine and morpholine) under the sealed-tube conditions to afford the corresponding 2,6-diaminoazulenes in excellent yields. Aromatic compounds with multiple-amino functional groups have been of great interest owing to their potential applications in organic electronic devices, such as hole transport materials for organic light-emitting diodes. 1 Therefore, a large number of synthetic procedures for aromatic compounds with multiple-amino groups were found in literatures. 2 In the pioneering works of azulene chemistry by Nozoe et al., 2,6-diaminoazulenes were first synthesized from an aminotropolone derivative, but the procedure requires a multistep reaction for the preparation of the starting tropolone derivatives which are essential to the preparation of 2,6-diaminoazulenes with different amino functions. 3 They have also reported that the most promising intermediate, diethyl 2-amino-6-bromoazulene-1,3-dicarboxylate (1) that could be obtained much easier, does not react with † Dedicated to Professor Isao Kuwajima on the occasion of his 77th birthday
2-Azulenyl trifluoromethanesulfonate was prepared by the reaction of 2-hydroxyazulene with trifluoromethanesulfonic anhydride in the presence of triethylamine as a base. Under the use of pyridine, 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate further reacted with 2-azulenyl trifluoromethanesulfonate to give 1-(1-trifluoromethanesulfonyl-1,4-dihydropyridin-4-yl)azulenyl trifluoromethanesulfonate. Moreover, we found that azulenes also reacted with 1-trifluoromethanesulfonylpyridinium trifluoromethanesulfonate to give 4-(1-azulenyl)-1,4-dihydropyridine derivatives and 6-(1-azulenyl)-1-trifluoromethanesulfonyl-1-aza-hexa-1,3,5-triene depending on the reaction conditions. 2-Azulenyl trifluoromethanesulfonate was converted finally into the parent azulene in excellent yield by palladium-catalyzed reduction using formic acid as a reducing reagent.
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