1,8-Diazabicyclo(5.4.0)undec-7-ene → 1-(6-Bromo-7-hydroxy-2-benzothiazolyl)-3-ethylurea

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A suspension of 1-(6,6-dibromo-7-oxo-4,5,6,7-tetrahydro-2-benzothiazolyl)-3-ethyl-urea 5 (7.78 g, 19.6 mmol) in THF (50 mL) was treated with DBU (8.79 mL, 58.8 mmol, 3.0 eq) dropwise at about 20° C. A dark green suspension was obtained while heat was generated upon addition of DBU. It was stirred at about 20° C. for about 18 hours. The reaction mixture was concentrated and the residue was treated with saturated NH4Cl (aq) solution to neutral. A light brown colored precipitate was obtained. It was filtered off and washed with H2O (2×50 mL), small amount of MeOH and CH2Cl2, and finally dried under vacuum to give 4.83 g (78%) of the desired compound 6. 1H NMR (DMSO) δ 10.68 (br s, 1H, NH), 7.43 (d, 1H, J=8.5 Hz, ArH), 7.08 (d, 1H, J=8.5 Hz, ArH), 6.70 (br s, 1H, NH), 3.18 (m, 2H, CH2), 1.09 (t, 3H, J=7.2 Hz, CH3). LC/MS 316 (MH+); RP-HPLC RT 2.80 minutes.

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