Ethylene Glycol → 1-[5-(2-Methyl-[1,3]dioxolan-2-yl)-furan-2-ylmethyl]-4-nitro-1H-pyrazole

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In a flame dried round-bottomed flask equipped with a magnetic stir bar and a Dean-Stark apparatus under inert atmosphere (N2), a solution of 1-[5-(4-nitro-pyrazol-1-ylmethyl)-furan-2-yl]-ethanone (3.40 g, 14.46 mmol), ethylene glycol (8.1 mL, 144.84 mmol) and TsOH (28 mg, 0.15 mmol) in toluene (150.0 mL) was heated to reflux for 4 h. The reaction mixture was allowed to cool to rt. Water (200 mL) and EA (40 mL) were added and the aq. phase was extracted with EA (2×80 mL). The combined org. extracts were washed with sat. aq. NaHCO3 (200 mL), dried over MgSO4, filtered, and the solvents were removed under reduced pressure. Purification of the residue by FC (60:40 hept-EA) gave the title compound as a yellow oil. TLC: rf (60:40 hept-EA)=0.31. LC-MS-conditions 02: tR=0.91 min. 1H NMR (400 MHz, CDCl3) δ 1.72 (s, 3H), 3.99 (dd, J=4.5, 2.5 Hz, 2H), 4.06 (dd, J=4.4, 2.5 Hz, 2H), 5.31 (s, 2H), 6.35 (d, J=3.3 Hz, 1H), 6.42 (d, J=3.3 Hz, 1H), 8.09 (s, 1H), 8.12 (s, 1H).

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