Ethylene Glycol → 1-[5-(2-Methyl-[1,3]dioxolan-2-yl)-furan-2-ylmethyl]-3-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-(3-nitro-pyrazol-1-ylmethyl)-furan-2-yl]-ethanone (1.760 g, 7.48 mmol), ethylene glycol (4.18 mL, 74.98 mmol) and TsOH (14 mg, 0.08 mmol) in toluene (74.8 mL) was heated to reflux for 4 h. The reaction mixture was allowed to cool to rt. Water (125 mL) and EA (25 mL) were added and the aq. phase was extracted with EA (2×50 mL). The combined org. extracts were washed with sat. aq. NaHCO3, 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)=022. LC-MS-conditions 02: tR=0.92 min; [M+H]+=280.04. 1H NMR (400 MHz, CDCl3) δ 1.71 (s, 3H), 3.95-4.02 (m, 2H), 4.02-4.09 (m, 2H), 5.36 (s, 2H), 6.33 (d, J=3.3 Hz, 1H), 6.41 (d, J=3.0 Hz, 1H), 6.91 (d, J=2.5 Hz, 1H), 7.48 (d, J=2.3 Hz, 1H).

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