Abstract
An efficient synthesis of 1-heteroaryl- and 1,3-bis(heteroaryl)azulenes was established by electrophilic substitution. The reaction of azulenes and 1,1'-biazulene with the triflate of N-containing heteroarenes proceeded smoothly in the presence of excess heteroarenes to afford the corresponding 1-dihydroheteroaryl- and 1,3-bis(dihydroheteroaryl)azulene derivatives in good yields. The 1-dihydroheteroaryl- and 1,3-bis(dihydroheteroaryl)azulene derivatives were readily converted into the desired 1-heteroaryl- and 1,3-bis(heteroaryl)-azulenes by treatment with tBuOK in DMSO or KOH in EtOH in excellent yields. The pyridinium salts 26 + ·I ― and 27 2+ ·2I ― were also prepared by the reaction of 4a and 5a with methyl iodide. 1-Heteroaryl- and 1,3-bis(heteroaryl)azulenes exhibited a significant color change in acetic acid from that in dichloromethane due to the development of intramolecular charge-transfer (CT) absorption bands.
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