[NH2:1][C:2]1[CH:6]=[CH:5][O:4][C:3]=1[C:7]([O:9][CH3:10])=[O:8].ClS([N:15]=[C:16]=[O:17])(=O)=O.[C:18]([O-])(O)=O.[Na+]>ClCCl>[NH:1]([C:2]1[CH:6]=[CH:5][O:4][C:3]=1[C:7]([O:9][CH2:10][CH3:18])=[O:8])[C:16]([NH2:15])=[O:17]To a solution of methyl 3-aminofuran-2-carboxylate 34 (100 mg, 1.0 eq) in dichloromethane (3 ml) at −78° C. was added chlorosulfonyl isocyanate (0.09 ml, 1.4 eq) dropwise. The reaction was slowly warmed to room temperature and stirred for 40 minutes. Reaction was concentrated. To the residue was added 6N HCl (3.5 ml) and mixture was heated to 100° C. for 20 minutes. Reaction mixture was allowed to cool down to room temperature, and was neutralized with saturated aq. NaHCO3. Solid was collected by filtration to yield ethyl 3-ureidofuran-2-carboxylate 35 (120 mg, 92%) as a beige solid which was used in the next reaction without further purification.
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