5,6-Dihydro-4H-pyrrolo[1,2-b]pyrazole

Uses

5,6-Dihydro-4H-pyrrolo[1,2-b]pyrazole is used in the preparation of withasomnine molecules, pyrazole alkaloids, for their application towards antiinflammatory compounds and analgesics.

Synthesis

3-(3-Chloropropyl)-1H-pyrazole (500 mg, 3.5 mmol) was used as a starting material and dissolved in a mixed solvent of isopropanol/water (5 mL/1 mL) and potassium hydroxide (389 mg, 6.9 mmol) was added. The reaction mixture was stirred at 90 °C for 2 hours. After completion of the reaction, the mixture was cooled to room temperature and extracted with dichloromethane (3 x 20 mL). The organic layers were combined, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. Purification of the residue by silica gel column chromatography (petroleum ether: ethyl acetate = 6:1 to 2:1) afforded 5,6-dihydro-4H-pyrrolo[1,2-B]pyrazole (150 mg, 39.6% yield) as a brown oil.LC-MS (ESI) detection: 109 [M + 1].

References

[1] Patent: WO2017/35353, 2017, A1. Location in patent: Paragraph 0953
[2] Tetrahedron Letters, 1996, vol. 37, # 7, p. 1095 - 1096
[3] Patent: WO2013/52394, 2013, A1. Location in patent: Paragraph 00248
[4] Tetrahedron, 2013, vol. 69, # 34, p. 7139 - 7146
[5] Patent: WO2013/192125, 2013, A1. Location in patent: Page/Page column 135