An ethanol solution of 12-oxatricyclo [7.2. 1.0 2, 8] dodeca-2 (8), 3, 6, 10-tetraen-5-one was irradiated with a 100-W Hg lamp through pyrex filter to give 8H-3-oxaheptalen-8-one, an oxepine condensed with tropone, in good yield together with a slight amount of 6- hydroxyazulene.