[C:1]([C:5]1[CH:6]=[CH:7][C:8]([OH:16])=[C:9]([C:11]([CH3:15])([CH3:14])[C:12]#[N:13])[CH:10]=1)([CH3:4])([CH3:3])[CH3:2].CCN(C(C)C)C(C)C.Cl[C:27]([O:29][CH3:30])=[O:28]>CN(C1C=CN=CC=1)C.C(Cl)Cl>[C:27](=[O:28])([O:29][CH3:30])[O:16][C:8]1[CH:7]=[CH:6][C:5]([C:1]([CH3:4])([CH3:2])[CH3:3])=[CH:10][C:9]=1[C:11]([C:12]#[N:13])([CH3:15])[CH3:14]
To a stirred mixture of compound 15 (126.6 g, 0.564 mol), DMAP (6.0 g) and DIEA (188 g, 1.46 mol) in anhydrous DCM (1500 mL) was added dropwise methyl chloroformate (110 g, 1.17 mol) in anhydrous DCM (300 mL) at 0° C. within 2 hours. After stirring for 12 hours at 0° C., ice-water (1.5 L) was added and the mixture was stirred at 0° C. for 30 minutes. The organic layer was separated and washed with 1 N HCl, water, and brine. The DCM solution was dried over MgSO4 and concentrated in vacuo to give compound 16 as a yellow solid. 1H NMR (DMSO-d6; 400 MHz) δ 7.47 (m), δ 7.39 (d), δ 7.24 (d), δ 3.84 (s), δ 1.71 (s), δ 1.30 (s).
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