81945-73-5

1H-Pyrazol-1-ol, is an intermediate in the synthesis of various pharmaceutical compounds containing pyrazole. It can be used for the construction of multidentate ligands.

General procedure for the synthesis of 1-hydroxypyrazole from pyrazole: Example 56: Preparation of N-[6-(2-hydroxy-2H-pyrazol-3-yl)-2,4-dioxo-7-trifluoromethyl-1,4-dihydro-2H-quinazolin-3-yl]-methanesulfonamide; 1. a mixture of pyrazole (10 g, 147 mmol) and mCPBA (36.2 g, 147 mmol) in ethyl acetate (500 mL) was stirred at room temperature for 10 days. 2. the reaction solution was concentrated in vacuum to give a yellow paste. 3. The paste was extracted with water (6 x 100 mL) and concentrated hydrochloric acid (100 mL). 4. The aqueous phase was washed with dichloromethane (2 x 100 mL). 5. 5. Combine the organic layers, concentrate in vacuum, and extract with concentrated hydrochloric acid (50 mL). 6. The aqueous phases were combined, trisodium phosphate dodecahydrate (115 g) was added, and then sodium hydroxide was added to adjust the pH to 10. 7. The aqueous phase was concentrated under vacuum to a volume of 400 mL, then extracted continuously with a solvent mixture of ether/dichloromethane (2/3) for 40 hours. 8. The organic phase was concentrated under vacuum and the residue was dissolved in chloroform. 9. The insoluble material was removed by filtration and the filtrate was washed with chloroform. 10. The aqueous phase was acidified with concentrated hydrochloric acid (200 mL) and then continuously extracted with a solvent mixture of dichloromethane/ether (2/3) for 70 hours. 11. The organic phases were combined and concentrated in vacuum to give 1-hydroxypyrazole (4.7 g, 38% yield) as a yellow slurry.

[1] Journal of the Chemical Society, Perkin Transactions 1: Organic and Bio-Organic Chemistry (1972-1999), 1995, # 3, p. 243 - 248
[2] Liebigs Annalen, 1995, # 8, p. 1563 - 1566
[3] Patent: WO2006/108591, 2006, A1. Location in patent: Page/Page column 113-114