[Br:1][C:2]1[CH:3]=[N:4][NH:5][CH:6]=1.Cl[CH:8]1[CH2:11][CH:10]([C:12]([O:14][CH3:15])=[O:13])[CH2:9]1.C(=O)([O-])[O-].[K+].[K+]>CN(C=O)C.C(OCC)C>[Br:1][C:2]1[CH:3]=[N:4][N:5]([CH:8]2[CH2:11][CH:10]([C:12]([O:14][CH3:15])=[O:13])[CH2:9]2)[CH:6]=1A mixture of 4-bromo-1H-pyrazole (500 mg, 3.40 mmol), methyl 3-chlorocyclobutanecarboxylate (607 mg, 4.08 mmol), and potassium carbonate (1.18 g, 8.50 mmol) in DMF (5 mL) was heated to 70° C. for 24 hours. The reaction mixture was cooled to ambient temperature and diluted with diethyl ether (200 mL). The mixture was washed with water (2×50 mL) and then brine (25 mL). The organic layer was dried over magnesium sulfate, filtered, and concentrated under reduced pressure to afford the crude product residue. The crude product residue was purified by column chromatography on silica (0-100% diethyl ether/hexanes) to afford methyl 3-(4-bromo-1H-pyrazol-1-yl)cyclobutanecarboxylate (Isomer 1) and methyl 3-(4-bromo-1H-pyrazol-1-yl)cyclobutanecarboxylate (Isomer 2). Methyl 3-(4-bromo-1H-pyrazol-1-yl)cyclobutanecarboxylate (Isomer 1): MS ESI calc'd. for C9H12BrN2O2 [M+H]+ 259 and 261. found 259 and 261. 1H NMR (500 MHz, DMSO-d6) δ 8.09 (s, 1H), 7.59 (s, 1H), 5.02-4.95 (m, 1H), 3.65 (s, 3H), 3.20-3.14 (m, 1H), 2.75-2.66 (m, 2H), 2.64-2.56 (m, 2H).
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