Hydrochloric Acid → 4-phenyl-1H-pyrazole hydrochloride

Trityl chloride (1.58 g, 5.67 mmol) was added to a stirred cold (0-5° C.) solution of 4-iodo pyrazole (1 g, 5.15 mmol) and triethylamine (1.04 g, 10.3 mmol) in DCM (12 mL). Stirring was continued at room temperature overnight. Cold water was then added and the product was extracted with DCM and the organic layer was washed with saturated sodium bicarbonate solution followed by brine. The organic phase collected was dried over Na2SO4 and concentrated under reduced pressure The residue was purified by column chromatography (using neutral alumina and 2% EtOAc in hexane as eluent) to afford 1.9 g (84.4% Yield) of 4-iodo-1-trityl-1H-pyrazole. Na2CO3 (727 mg, 6.86 mmol) was added to a stirred solution of 4-iodo-1-trityl-1H-pyrazole (1.5 g, 3.43 mmol) in toluene: H2O (4:1, 20 mL). Pd(PPh3)4 (790 mg, 0.686 mmol) and phenylboronic acid (838 mg, 6.86 mmol) were then added and the reaction mixture was heated to reflux for 2 hrs. The reaction mixture was then diluted with water and the product was extracted with ethyl acetate. The organic layer was washed with saturated brine solution, dried over sodium sulfate and concentrated to in vacuo. Purification by column chromatography (using neutral alumina and 5% EtOAc in hexane as eluent) afforded 790 mg (59.4% Yield) of 4-phenyl-1-trityl-1H-pyrazole. 1H NMR (300 MHz, CDCl3): δ 7.96-7.94 (s, 1H), 7.64-7.6 (s, 1H), 7.46-7.4 (d, 2H), 7.36-7.0 (m, 11H), 7.24-7.16 (m, 7H). A solution of 4-phenyl-1-trityl-1H-pyrazole (785 mg, 2.03 mmol) in ether.HCl (15 mL) was stirred for 1 hr. The reaction mixture was then concentrated under reduced pressure and washed with hexane to afford 320 mg (87.4% Yield) of 4-phenyl-1H-pyrazole hydrochloride. 1H NMR (300 MHz, DMSO-d6): δ 8.1-8.08 (s, 2H), 7.64 (d, 2H), 7.38 (t, 2H), 7.22 (t, 1H).