NITROSATION OF ALPHA,BETA-UNSATURATED OXIMES .4. SYNTHESIS AND STRUCTURE OF 3,4-DIAZACYCLOPENTADIENONE DERIVATIVES

β-Alkyl or aryl α,β-unsaturated oximes are converted by nitrous acid under oxygen or by a mixture of nitrous and nitric acids into 3,4-diazacyclopentadienone dioxides (3). Some negatively substituted methylene ketones are oxidized by nitrous acid to the same heterocycles. Nitrosation of the oximes under nitrogen produced the corresponding heterocyclic oxime. Nitrosation of 1-hydroxypyrazole 2-oxides (10) yielded 4-nitropyrazolenine 1,2-dioxides (11) that decomposed thermally to 3. Reduction of the dioxides 3 with zinc in acetic acid furnishes a new and general route to 4-hydroxypyrazoles. Reduction of 3 with sodium dithionite yields 1,4-dhydroxypyrazoles, a new class of organic compounds. Oxidation of these latter compounds yields 3,4-diazacyclopentadienone oxides (6). A general mechanism for the nitrosation of α,β-unsaturated oximes is presented. © 1969, American Chemical Society. All rights reserved.