N#N.C([O-])([O-])=O.[K+].[K+].[CH2:9]([O:11][C:12]([C:14]1[N:15]=[C:16]([CH2:19]OS(C)(=O)=O)[O:17][CH:18]=1)=[O:13])[CH3:10].[Br:25][C:26]1[CH:27]=[N:28][NH:29][CH:30]=1>CCCC[N+](CCCC)(CCCC)CCCC.[Br-].CC(C)=O>[CH2:9]([O:11][C:12]([C:14]1[N:15]=[C:16]([CH2:19][N:28]2[CH:27]=[C:26]([Br:25])[CH:30]=[N:29]2)[O:17][CH:18]=1)=[O:13])[CH3:10]In a flame dried round-bottomed flask equipped with a magnetic stir bar and under inert atmosphere (N2), K2CO3 (356 mg, 2.55 mmol) was added at rt to a solution of 2-methanesulfonyloxymethyl-oxazole-4-carboxylic acid ethyl ester (127 mg, 0.51 mmol), TBAB (33 mg, 0.10 mmol) and 4-bromo-1H-pyrazole (76 mg, 0.51 mmol) in acetone (5.0 mL). After stirring at rt for 2 h, the solvent was removed under reduced pressure. The residue was partitioned between water and EA, the two layers were separated and the aq. layer was extracted twice with EA. The combined org. extracts were dried over Na2SO4, filtered, and the solvent was removed under reduced pressure to give the title compound as an orange solid. TLC: rf (1:1 hept-EA)=0.27. LC-MS-conditions 01: tR=0.84 min, [M+H]+=299.96.
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