Oxidation of 5, 5′-biguaiazulene-3, 3′(5H, 5′ H)-dione (2) with 2, 3-dichloro-5, 6-dicyano- p-benzoquinone (DDQ) in CH 2 Cl 2 at 25° C under aerobic conditions rapidly gives the title compound, 5-isopropylidene-3, 8-dimethyl-1 (5H)-azulenone (4), in 52% isolated yield. The crystal structure of 4 is reported as the first example for azulenequinonemethides.