N-2-H-Tetrafluoroethylpyrazole (1c). Potassium metal (0.2 g, 5 mmol) was added to a solution of
pyrazole (6.8 g, 100 mmol) in anhydrous THF (30 ml). After solution of the metal a current of
tetrafluoroethylene was passed through with vigorous stirring for 20-25 h at such a rate that the gas was
completely absorbed, maintaining the temperature of the reaction mixture at 35-45°C. The THF was distilled off
with an efficient fractionating column, and the fraction of bp 90-110°C was collected. The crude product,
containing solvent as contaminant, was stirred with water (20 ml) and ether (20 ml), and extracted. The ether
layer was separated, dried over MgSO , and the ether was distilled off at atmospheric pressure with a
4
fractionating column. The residue was redistilled, collecting the fraction of bp 107-112°C.
N-2-H-Tetrafluoroethyl-3,5-dimethylpyrazole (1d) was obtained analogously to compound 1c. After
distillation of THF the residue was redistilled in vacuum. The data corresponded with those described in [8].
N-Difluoromethyl-4-nitropyrazole (2a). Pyrazole 1a (1.18 g, 10 mmol) was added with stirring to a
mixture of H SO (d = 1.84) (3 ml) and HNO (d = 1.52) (2 ml). The reaction mixture was stirred for 3 h at
2
4
3
3
0-40°C, and left overnight. The mixture was poured onto ice, neutralized with sodium carbonate solution,
extracted with ether (3 × 20 ml), the ether extract was washed with water (3 × 50 ml), dried over MgSO , the
4
ether distilled off, and the residue distilled in vacuum.
N-Difluoromethyl-3,5-dimethyl-4-nitropyrazole (2b). Chlorodifluoromethane was bubbled with
vigorous stirring through a solution of 3,5-dimethyl-4-nitropyrazole (1.4 g, 10 mmol) in a mixture of dioxane
(
(
10 ml), water (7 ml), and KOH (2.9 g, 50 mmol) at 40-45°C until the end of gas absorption (~4 h). Water
50 ml) was added, the precipitated crystals were filtered off, dried in the air, and crystallized from hexane.
N-2-H-Tetrafluoroethyl-4-nitropyrazole (2c) was obtained analogously to compound 2a.
N-2-H-Tetrafluoroethyl-3,5-dimethyl-4-nitropyrazole (2d). Pyrazole 1d (1.96 g, 10 mmol) was added
with stirring to a mixture of H SO (d = 1.84) (3 ml), HNO (d = 1.52) (2 ml), and 10% oleum (0.5 ml). The
2
4
3
reaction mixture was stirred for 3 h at 100-110°C, and left overnight. The mixture was then treated analogously
to compound 2a.
N-Polyfluoroalkyl-4-bromopyrazoles (3a-d). Bromine (3.2 g, 20 mmol) was added with vigorous
stirring to a mixture of the appropriate compound 1a-d (20 mmol) and water (20 ml), and the mixture stirred at
room temperature until decoloration of the reaction mixture. The mixture was extracted with ether (3 × 20 ml),
the ether extract was washed with water (3 × 50 ml), with 2% NaHSO solution (50 ml), and once again with
3
water (50 ml). The extract was dried over MgSO , the ether distilled off, and the residue distilled in vacuum.
4
N-Difluoromethyl-4-chloro-3,5-dimethylpyrazole (4b). Sodium bicarbonate (1.68 g, 20 mmol) was
added with vigorous stirring to a mixture of pyrazole 1b (2.92 g, 20 mmol) and water (30 ml), and the mixture
stirred at room temperature while passing a current of chlorine until saturation (~30 min). The mixture was
extracted with ether (3 × 20 ml), the ether extracts washed with water (3 × 50 ml), with 2% NaHSO solution (50
3
ml), and once again with water (50 ml). The extract was dried over MgSO , the ether distilled off, and the
4
residue redistilled in vacuum.
N-2-H-Tetrafluoroethyl-4-chloro-3,5-dimethylpyrazole (4d) was obtained analogously.
N-Difluoromethyl-4-iodo-3,5-dimethylpyrazole (5b). N-Iodosuccinimide (4.75 g, 21 mmol) was added
with stirring to a solution of pyrazole 1b (2.9 g, 20 mmol) in 90% H SO (15 ml). The mixture was stirred at 30-
2
4
3
5°C until the appearance of an intense color of iodine, then poured onto ice, and extracted with ether (3 × 20
ml). The combined ether extract was washed with water (3 × 50 ml), with 5% NaHSO solution (50 ml), and
3
once again with water (50 ml). The solution was dried over MgSO , the ether distilled off and the residue
4
distilled in vacuum.
N-2-H-Tetrafluoroethyl-4-iodopyrazole (5c) and N-2H-Tetrafluoroethyl-4-iodo-3,5-dimethyl-
pyrazole (5d) were obtained analogously.
N-Difluoromethyl-4-cyano-3,5-dimethylpyrazole (6b). Copper(I) cyanide (2.7 g, 30 mmol) was added
to a solution of pyrazole 5b (2.9 g, 20 mmol) in anhydrous dimethylacetamide (15 ml). The reaction mixture was
boiled with stirring for 20 h. Water (100 ml) was then added, the product was extracted with ether, and separated
chromatographically (silica gel MN-Kieselgel-60, eluent chloroform, R 0.8).
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