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Cyclocondensation of 2‐(hydroxyimino)‐1‐(naphthalen‐1‐yl)butane‐1,3‐dione with alkyl hydrazines leading to new 1‐alkyl‐3(5)‐methyl‐5(3)‐(naphthalene‐1‐yl)‐4‐nitrosopyrazoles is described. 8 previously unknown N‐alkyl‐4‐nitrosopyrazoles with a 1‐naphthalene substituent at the 3 or 5 position of the pyrazole ring were obtained as a result. It was found that yields of naphthyl‐substituted pyrazoles with N‐alkyl groups near the naphthalene substituent were significantly lower than for 3‐(naphthalen‐1‐yl)‐substituted pyrazoles. Particular yields of pairwise formed isomeric nitrosopyrazoles were associated with the different electrophilicity of the two carbonyl groups of the initial diketone. Using quantum chemical calculations by the DFT method B3LYP−D3/6‐311G(d,p), the potential energies of the various conformers were estimated to draw a conclusion about the preferred attack of alkyl hydrazine on the carbonyl group, associated with the naphthalene ring. 1H NMR and 2D 1H‐13C HSQC spectra of the compounds confirmed this direction of the reaction. The crystal structures of the synthesized compounds were established by X‐ray powder diffraction technique. Crystal structure data were in agreement with quantum chemical calculations.

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This article describes the regioselective synthesis of novel nitroso-pyrazolylquinoxalines via cyclocondensation of 2-hydroxyimino-1,3-diketones with hydrazinylquinoxalines. Of note, this is the first time that 2-hydroxyimino-1,3-diketones are used as electrophilic reagents to...