Novel and facile synthesis of β-(4-azuleno[1,2-b]thienyl)- and β-(4-azuleno[2,1-b]thienyl)-α,β-unsaturated ketones by intramolecular tropylium ion-mediated furan ring-opening reaction

The novel and efficient methods for the synthesis of β-(4-azuleno[1,2-b]thienyl)-α,β-unsaturated ketones () and β-(4-azuleno[2,1-b]thienyl)-α,β-unsaturated ketones () have been described. Refluxing the dichloromethane solutions of 2-tropylio-3-(2-furyl)thiophene tetrafluoroborates () or 3-tropylio-2-(2-furyl)thiophene tetrafluoroborates () afforded () and (), respectively, in moderate yields. The reaction involves an intramolecular tropylium ion-mediated furan ring-opening reaction.