[CH3:1][O:2][C:3]1[CH:11]=[CH:10][C:6]([C:7](N)=[O:8])=[C:5]([CH3:12])[CH:4]=1.[CH3:13][N:14]([CH:16](OC)OC)[CH3:15].C(Cl)Cl.CO.C([O-])(=O)C.[NH4+:30]>C1COCC1>[CH3:1][O:2][C:3]1[CH:11]=[CH:10][C:6]([C:7]([C:16]([N:14]([CH3:15])[CH3:13])=[NH:30])=[O:8])=[C:5]([CH3:12])[CH:4]=11G (296.15 g, 1.794 mol) was dissolved in THF (1.5 L) in a flask equipped with a mechanical stirrer and distillation head to give a thick slurry. DMF-DMA (263 mL, 1.1 eq) was added in one portion and slowly heated to gentle reflux. After 30 min at reflux, the reaction mixture became a homogeneous solution. The reaction was maintained at reflux for 1.5 h, and checked by HPLC and TLC (10:1 CH2Cl2/MeOH). At atmospheric pressure, 1150 mL THF was distilled out and replaced with 1500 mL heptane (Note that if the solution is not quite saturated, remaining THF should be removed by distillation). The remaining solution was cooled slowly to rt overnight with stirring, seeded at 68° C. Rapid crystallization was observed. The resulting slurry was cooled to 0° C., filtered and washed with heptanes (500 mL) and dried under vacuum at rt for 48 h. 384.6 g (97.4%) of 1H was isolated as a light tan crystalline solid. HPLC-MS using a neutral buffer ammonium acetate buffer system showed only a single peak, with the expected mass.
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