COPPER POWDER–CATALYZED C-N BONDS
919
column (Shimadzu, fused silica capillary column, 0.33 mm ꢁ 25 m, 0.25 mm film
thickness) using nitrogen as carrier gas. The isolation of pure products was carried
out via thin-layer (silica gel 60 GF254, Merck) chromatography. All hydrazones 1
were prepared by the reported method.[11] Copper powder (100 mesh, 99.5%) was
purchased from Strem. Commercially available organic and inorganic compounds
were used without further purification.
General Procedure for Copper Powder–Catalyzed Synthesis of
1-Aryl-1H-indazoles and Their Analogs
Hydrazone 1 (0.5 mmol), copper powder (0.05 mmol), NaOtBu (0.096 g,
1 mmol), and PEG-400 (3 mL) were added to an organic reactor (Radleys Discovery
Technologies). After the system was flushed with N2, the mixture was stirred at
110 ꢀC for an appropriate time. The reaction mixture was cooled down to room tem-
perature, poured into water, and extracted with ethyl acetate. The combined organic
layer was dried over Na2SO4 and concentrated under reduced pressure. The crude
mixture was purified by thin-layer chromatography (silica gel, ethyl acetate–hexane
mixture) to give 1-aryl-1H-indazoles and its analogs 2. All products prepared by this
procedure were characterized by GLC, melting point, and spectroscopic comparison
with authentic samples synthesized by the method of recent reports.[9,11,16,20] Spec-
troscopic data for new products are shown.
1-(3-Chlorophenyl)-1H-indazole (2f)
1
Oil. H NMR (400 MHz, CDCl3) d 7.24–7.28 (m, 1H), 7.32–7.35 (m, 1H),
7.45–7.49 (m, 2H), 7.65–7.67 (m, 1H), 7.76–7.83 (m, 3H), 8.22 (d, J ¼ 0.8 Hz, 1H).
13C NMR (100 MHz, CDCl3) d 110.5, 120.6, 121.7, 122.1, 122.9, 125.7, 126.8,
127.8, 130.7, 135.4, 136.3, 138.8, 141.5. Anal calcd. for C13H9ClN2: C, 68.28; H,
3.97; N, 12.25. Found: C, 68.25; H, 4.14; N, 12.33.
1-(2-Fluorophenyl)-1H-indazole (2h)
1
Solid, mp 83–85 ꢀC (hexane–ethyl acetate). H NMR (400 MHz, CDCl3) d
7.22–7.26 (m, 1H), 7.30–7.35 (m, 2H), 7.39–7.46 (m, 3H), 7.61–7.65 (m, 1H), 7.81
(dt, J ¼ 8.1 and 1.0 Hz, 1H), 8.26 (d, J ¼ 0.8 Hz, 1H). 13C NMR (100 MHz, CDCl3)
d 110.7 (d, J ¼ 5.1 Hz), 117.2 (d, J ¼ 19.6 Hz), 121.3, 121.7, 124.9 (d, J ¼ 23.3 Hz),
125.1, 127.4, 127.8 (d, J ¼ 11.6 Hz), 128.1, 129.4 (d, J ¼ 8.0 Hz), 136.4, 140.3, 156.3
(d, J ¼ 251.0 Hz). Anal. calcd. for C13H9FN2: C, 73.57; H, 4.27; N, 13.20. Found:
C, 73.58; H, 4.34; N, 13.11.
1-(2,5-Dichlorophenyl)-1H-indazole (2i)
1
Oil. H NMR (400 MHz, CDCl3) d 7.24–7.29 (m, 2H), 7.40–7.46 (m, 2H),
7.53–7.55 (m, 2H), 7.82 (d, J ¼ 8.1 Hz, 1H), 8.25 (d, J ¼ 0.8 Hz, 1H). 13C NMR
(100 MHz, CDCl3) d 110.7, 121.5, 121.9, 124.6, 127.5, 129.7, 129.9, 130.0, 131.8,
133.4, 136.5, 138.2, 140.3. Anal. calcd. for C13H8Cl2N2: C, 59.34; H, 3.06; N,
10.65. Found: C, 59.48; H, 3.13; N, 10.40.