The reaction of diketene with diazoacetone (2) in the presence of benzophenone under irradiation afforded trans-1-acetyl-5-oxo-4-oxaspiro [2, 3] hexane (3) in 22% yield. Similarly, the photolysis of diketene and 2-diazoesters such as ethyl 2-diazo-3-oxo-butanoate (4a) and ethyl 2-diazo-3-oxohexanoate (4b), followed by treatment with absolute methanol saturated with dry hydrogen chloride gave diesters ; e.g., methyl 3, 6-dioxo-5-ethoxycarbonylhexanoate (8a) (39%) and methyl 3, 6-dioxo-5-ethoxycarbonylnonylate (8b) (30%), and/or furan derivatives ; e.g., 3-ethoxycarbonyl-5-methoxycarbonylmethyl-2-methylfuran (9a) (35%) and 3-ethoxycarbonyl-5-methoxycarbonylmethyl-2-propylfuran (9b) (33%). A similar reaction of diketene with di-tert-butyl diazomalonate (10) gave rise to dimethyl 2-methoxycarbonyl-4-oxohexane-1, 6-dioate (12) in 58% yield.