Formation of Azulenequinone Derivatives from Variously Functionalized Azulenes by Bromine-oxidation

Article abstract of DOI:10.1002/jccs.199700002

Variously functionalized 1,5- and 1,7-azulenequinones were easily derived in one-pot in 30-50% yield from the bromine-oxidation of 2-methoxyazulene and 2-methyl derivatives of 1-cyano-, 1-methoxycarbonyl- and its 7-isopropyl derivatives, while 1-methoxycarbonylazulene afforded several unstable products from which we could not isolate any azulenequinones. 1-Acetylazulene afforded 3-bromo-1,5- and -1,7-azulenequinones via side-chain brominated intermediates in high yield. 1,3-Dichloroazulene afforded a mixture of 3-chloro-1,5- and -1,7-azulenequinones, while 1-fluoro- and 1,3-diiodoazulene gave a mixture of 3-bromoazulenequinones. Analogous oxidation of 1,3-difluoroazulene produced 3-fluoroazulenequinones, but we could not isolate them due to its instability. Hydroxy group of 2-(3-hydroxypropyl)azulene was intact during this quinone formation reaction.