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Six analogues and derivatives (1-6) of 3-phenylhydrazonopentane-2,4-dione (7) were subjected to gas-phase thermolysis. The Arrhenius log A and Ea (kJ ) of the Ϫ1 Ϫ1(s ) mol analogues (1-5) are, respectively: 10.42 and 140.8 for 1-cyano-1-phenyl-hydrazonopropanone (1), 11.19 and 135.4 for 1-cyano-1-(p-nitrophenylhydrazono)-propanone (2), 10.68 and 144.9 for 1-cyano-1-(p-methoxyphenylhydrazono)propanone (3), 11.76 and 137.8 for 1-cyano-3-phenyl-1-phenylhydrazonopropanone (4), and 11.29 and 145.9 for 1-cyano-1-phenylhydrazonobutanone (5). The corresponding values for ethyl 3-oxo-2-phenylhydrazonobutanoate (6) are 11.90 and 143.3 kJ The rates of reaction at are compared with those of Ϫ1 Ϫ1 s mol . 600 K the title diketone (7) and of pentane-2,4-dione (8) and rationalized in terms of a plausible elimination pathway involving a semiconcerted six-membered transition state.

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New Synthetic Approaches to Condensed Pyridazinones: Alkylpyridazinyl Carbonitriles (V) as Building Blocks for the Synthesis of Condensed Pyridazinones.--(AL-AWADHI, H.; AL-OMRAN, F.; ELNAGDI, M. H.; INFANTES, L.; FOCES-FOCES, C.; JAGEROVIC, N.; ELGUERO, J.; Tetrahedron 51 (1995) 46, 12745-12762; Dep. Chem., Fac. Sci., Univ. Kuwait, Safat 13060, Kuwait; EN)