Nitrosation of lithium 1,3-diketonates bearing fluoroalkyl and aryl (or hetaryl) substituents in positions 1 and 3 results in 3-polyfluoroalkyl-1,2,3-propanetrione 2-oximes (from this point on, oximes). Under similar conditions, lithium (Z)-1,1,1-trifluoro-4-oxo-4-(thien-2-yl)-2-buten-2-olate forms a hydration product of the corresponding oxime. Nitrosation of fluoroalkyl-containing lithium 1,3-diketonates is accompanied by retro-decomposition of the initial lithium 1,3-diketonates and the target oximes (or their hydration products) followed by oxidation and hydrolysis of the reaction products. Under the GC-MS conditions, the oximes undergo partial thermal decomposition to 2-aryl(hetaryl)-2-oxoethanenitriles. An analysis of solutions of the oximes in DMSO-d6 by 1H and 19F NMR spectroscopies revealed isomerization and hydration of these compounds. The temperature ranges of stability of the oximes were determined by thermogravimetric analysis and differential thermal analysis. The molecular and crystal structures of 4,4-difluoro-1-(4-methoxyphenyl)-1,2,3-butanetrione 2-oxime and 4,4,4-trifluoro-1-(thien-2-yl)-1,2,3-butanetrione 2-oxime were determined by X-ray diffraction.