Br[C:2]1[CH:3]=[N:4][N:5]([CH:7]2[CH2:12][CH2:11][CH2:10][CH2:9][O:8]2)[CH:6]=1.[Li]CCCC.CN([CH:21]=[O:22])C.O>C1COCC1>[O:8]1[CH2:9][CH2:10][CH2:11][CH2:12][CH:7]1[N:5]1[CH:6]=[C:2]([CH:21]=[O:22])[CH:3]=[N:4]1
4-Bromo-1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazole (61 g, 0.264 mol) was dissolved in THF (400 mL). Then 1.6 M n-BuLi (181 mL) was added to the solution which was at −95° C. The reaction mixture was stirred over a period of 45 minutes at the same temperature. Then DMF (22.4 mL, 0.29 mol) was added (the same temperature was maintained). The mixture was allowed to heat up to room temperature before addition of water (100 mL). The organic layer was separated, and the aqueous phase was extracted with ether (3×50 mL). The combined organic extracts were dried over Na2SO4, filtered and evaporated. The residue was purified by chromatography (EtOAc/hexane, 1:4) to afford 1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazole-4-carbaldehyde (29 g, 57%).
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