STABILITY, DECOMPOSITION, AND REACTIVITY OF A 1,2-DIAZACYCLOPENTENE-3,5-DIONE - 4,4-DIETHYLPYRAZOLINE-3,5-DIONE

The diazacyclopentene-3,5-dione, 4,4-diethylpyrazoline-3,5-dione (2), was prepared by the oxidation of 4,4- diethylpyrazolidine-3,5-dione (1) with either nitrogen tetroxide or lead tetraacetate (LTA). Dilute solutions of 2 proved to be more stable when nitrogen tetroxide was used to oxidize 1 and could be stored for indefinite periods at –15°. On warming to room temperature, 2 decomposed readily to give products which depended on the nature of the oxidant and decomposition conditions. Oxidation of 1 with nitrogen tetroxide and decomposition gave nitrogen, 2,2,6,6-tetraethylpyrazolo[1,2-a]pyrazole-1,3,5,7-tetraone (3), 1-(diethylcarboxyacetyl)-4,4-diethylpyrazolidine- 3,5-dione (4), and diethylmalonic acid (5) as products. Oxidation of 1 with LTA and decomposition gave nitrogen, 3, lead diethylmalonate (9), 3-acetoxy-4,4-diethyl-2-pyrazolin-5-one (10), 3,5-diacetoxy-4,4-diethylpyrazole (11), and diacetoxy diethylmalonate (13) as products. The in situ reaction of 2 with dienes yielded a series of Diels-Alder adducts. Adducts were obtained by the reaction of 2 with 2,3-dimethyl-1,3- butadiene, isoprene, 1,4-diphenyl-1,3-butadiene, cyclopentadiene, 1,3-cyclohexadiene, α-phellandrene, 1,3-cyclooctadiene, and anthracene. Higher yields of the adducts resulted when LTA was used to oxidize 1. The nmr and uv spectra of the adducts gave a considerable amount of information about their geometry. © 1969, American Chemical Society. All rights reserved.