[NH2:1][C:2]1[S:3][CH:4]=[C:5]([C:7]([O:9][CH2:10][CH3:11])=[O:8])[N:6]=1.[C:12](=O)([O:18]C(C)(C)C)[O:13][C:14]([CH3:17])([CH3:16])[CH3:15].CCCCC>C1COCC1.CN(C)C1C=CN=CC=1>[C:14]([O:13][C:12]([NH:1][C:2]1[S:3][CH:4]=[C:5]([C:7]([O:9][CH2:10][CH3:11])=[O:8])[N:6]=1)=[O:18])([CH3:17])([CH3:16])[CH3:15]Ethyl 2-aminothiazole-4-carboxylate 87 (10.0 g, 58.1 mmol) was taken up in 150 mL of anhydrous THF along with di-tert-butyl carbonate (12.67 g, 58.1 mmol) and 4-(dimethyl)aminopyridine (DMAP) (10 mg, 0.082 mmol). The reaction mixture was stirred at 50° C. for 4 h and then at room temperature for 18 h. It was then concentrated under reduced pressure to obtain a thick oil. Pentane was added and the resulting crystalline materials were collected by filtration and dried to afford 88 (10.5 g, 66% yield).
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