Pyridazine derivatives and related compounds. Part 14. Photolysis of 3-diazo-4,5-diphenylpyrazolo{[}3,4-c]pyridazine

The photochemistry of 3-cliazopyrazolopyriclazine has been investigated. The irradiation of 3-diazo-4,5-diphenylpyrazolo{[}3,4-clpyridazine in various solvents forms a carbene intermediate, which transforms into 3-substituted derivatives. For photolysis in the presence of acetylacetone or ethyl acetoacetate the coupling reactions which occur at the methylene group are faster than carbene formation, and can lead to direct cyclisation into condensed 1,2,4-triazines. Photolysis in the presence of diethyl malonate forms an acyclic hydrazone.