6-Azulyne, the first azulyne to be prepared, has been trapped with furan to give an adduct whose crystal structure reveals marked bondalternation in the azulene π system. The double bond in the furan moiety is responsible in part for the bond localization, as hydrogenation of that bond attenuates the effect. The regiochemistry of electrophilic attack on the adduct has been examined briefly, with results contrary