Base induced ring opening reactions of 2-(substituted)-4H-pyran-4-ones (R=H, Ph) gave the corresponding 5-(substituted)-3,5-dioxopentanals, which were in turn transdiazotized with 2-azido-1-ethylpyridin-1-ium BF4. The reactions gave 5-(substituted)-2,4-bis(diazo)-3,5-dioxopentanals and 4-(substituted)-1,3-bis(diazo)-2,4-butandiones, the latter being the deformylating diazo transfer products. A two-fold deformylation product (1,3-bisdiazo-2-propanone) was observed in the reaction of 3-oxopentandial, which was also synthesized from tosyl azide and 1,5-bis(N-methyl-N-phenylamino)-trans,tra 1,4-pentadiene-3-one in low yield. 4-(substituted)-3-diazo-2,4-butandieones also formed as side products. The reactions of 4,4-dimethoxy-3-oxobutanal and ethyl 2,4-dioxobutanoate with the same azidinium salt gave 1-diazo-3,3-dimethoxy-2-propanone and ethyl 3-diazo-2-oxopropanoate respectively.