Synthesis of 1-(pyridyl, quinolyl, and isoquinolyl)azulenes by Reissert–Henze type reaction

Azulene derivatives reacted with N-oxide of several heterocycles in the presence of trifluoromethanesulfonic anhydride (Tf2O) to afford 1-(pyridyl, quinolyl, and isoquinolyl)azulenes in good yield, respectively. In the case of the reaction with the 1-azulenyl methyl sulfide (12), 1,1′-biazulene derivative 13 was obtained under the similar reaction conditions. The first synthesis of unsymmetrical 1,3-di(pyridyl)azulene derivative was also established via our new preparation method following the electrophilic pyridinylation using the reaction with pyridine in the presence of Tf2O.