One Step Synthesis of 4,6,8-Trimethoxyazulenes - as Building Block for 2-Functionalized Azulenes.

Here we present a simple gold-catalyzed one-pot reaction of easily available diarylbutadiynes, with trimethoxybenzene as solvent and reactant to synthesize 4,6,8-trimethoxyazulenes. The methoxy substituents, which render the azulene very electron-rich, enable a change of azulenes typical regioselectivity for electrophilic substitutions, which enables facile electrophilic 2-substitution with iodine, bromine, chlorine, selenium or sulfur. Especially the 2-haloazulenes which can usually only be obtained through lengthy multistep syntheses are valuable building blocks for the synthesis of 2-substituted azulene derivatives.