1H-Indazole-5-boronic acid pinacol ester

Chemical Properties

1H-Indazole-5-boronic acid pinacol ester (also known as 5-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-indazole) is a light yellow solid powder at room temperature and pressure. It is an indazole compound poorly soluble in water but in common organic solvents, including dichloromethane, chloroform, ethyl acetate, etc. The chemical structure of this compound contains a multifunctional boric acid ester unit and exhibits excellent chemical conversion activity. It can undergo arylation, oxidation, and amination reactions under the catalysis of transition metals, and it has certain applications in synthesising functional organic molecules of indazole.

Synthesis

5-Bromoindazole (9.45 g, 48 mmol), bis(pinacolato)diboron (15.5 g, 61 mmol), potassium acetate (16.7 g, 170 mmol), and anhydrous DMF (160 mL) were added to the reaction flask under argon protection. Pd(dppf)Cl2-CH2Cl2 (985 mg, 1.2 mmol) was subsequently added as a catalyst. The reaction mixture was stirred at 90 °C for 24 hours. After completion of the reaction, it was cooled to room temperature, diluted with ethyl acetate (250 mL) and washed with water (2 x 50 mL). The organic phase was concentrated under reduced pressure and purified by silica gel column chromatography (eluent: hexane/ethyl acetate, 10:1, v/v, Rf = 0.6) to afford 1H-indazole-5-boronic acid pinacol ester (9.8 g, 84% yield). The product was confirmed by 1H NMR (300 MHz, CD3OD) and mass spectrometry (DCI/NH3).1H NMR data: δ 1.36 (s, 12H), 7.51 (dt, J = 8.5, 1.0 Hz, 1H), 7.73 (dd, J = 8.5, 1.0 Hz, 1H), 8.08 (d, J = 1.0 Hz, 1H), 8.23 ( t, J = 1.0 Hz, 1H). Mass spectral data: m/z 245 (M + 1)+.

References

[1] Patent: WO2009/67586, 2009, A1. Location in patent: Page/Page column 42
[2] Patent: CN105254613, 2016, A. Location in patent: Paragraph 0125; 0126; 0127
[3] Patent: KR2015/88007, 2015, A. Location in patent: Paragraph 0282; 0283; 0284
[4] Patent: KR101561332, 2015, B1. Location in patent: Paragraph 0117-0121
[5] Patent: KR101612160, 2016, B1. Location in patent: Paragraph 0114; 0115; 0116; 0117; 0118