[CH3:1][O:2][C:3](Cl)=[O:4].[C:6]1(=[O:12])[NH:10][C:9](=[O:11])[CH:8]=[CH:7]1.CN1CCOCC1>CCOC(C)=O>[CH3:1][O:2][C:3]([N:10]1[C:6](=[O:12])[CH:7]=[CH:8][C:9]1=[O:11])=[O:4]Methylchloroformate (4.4 mL, 56.7 mmol, 1 eq) was added to a solution of maleimide (5.5 g, 56.7 mmol, 1 eq) and NMM (6.2 mL, 56.7 mmol, 1 eq) in 200 mL of EtOAc at 0° C. The suspension was stirred at 0° C. for 30 minutes, filtered and washed with EtOAc. Filtrate and washings were combined and washed with cold water and dried over anhydrous Na2SO4. After filtration and evaporation under vacuum a pink solid was obtained. Purification by column chromatography on silica gel (Hexane-EtOAc, 1:1, v/v) provided the product (4.8 g, 55%).
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