Br[CH:2]([C:6](=O)[CH3:7])[C:3](=[O:5])[CH3:4].[NH2:9][C:10]([NH2:12])=[O:11].C([O-])(O)=O.[Na+].[Na+].[Cl-]>CC(C)=O.O.CCOC(C)=O>[NH2:12][C:10]1[O:11][C:2]([C:3](=[O:5])[CH3:4])=[C:6]([CH3:7])[N:9]=1
3-Bromo-2,4-pentandione (P8) (26.66 g, 148.93 mmol) obtained in Step I as described above, is dissolved in acetone (87 mL). This mixture is added to a solution of urea (22.36 g, 372 mmol, 2.5 eq) in water (20 mL). The resulting mixture is heated in order to obtain a clear solution and is distributed into 38 microwave tubes (3 ml each). The vials are heated to 100° C. for 1200 s each in the microwave oven. All vials are combined, NaHCO3 sat (100 ml) and EtOAc (100 ml) are added, the aqueous phase is saturated with NaCl and the phases are separated. The aqueous phase is extracted with EtOAc (4 times 100 ml). Combined organic layers are dried over MgSO4, filtrated and evaporated under reduced pressure to give 1-(2-amino-4-methyl-1,3-oxazol-5-yl)ethanone (P5) as an orange solid (12.09 g). It is further recrystallized in MeOH, affording a brownish solid (5.56 g, 27%). 1H NMR (DMSO-d6) δ: 2.22 (s, 3H), 2.25 (s, 3H), 7.51 (s, 2H).
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