[C:1]([O:4][C:5]1[CH:14]=[C:13]2[C:8]([C:9]([CH2:16][C:17]([OH:19])=[O:18])=[CH:10][C:11](=[O:15])[O:12]2)=[CH:7][CH:6]=1)(=[O:3])[CH3:2].[Cl:20][C:21]([Cl:25])([Cl:24])[CH2:22]O.C1(N=C=NC2CCCCC2)CCCCC1>ClCCl>[Cl:20][C:21]([Cl:25])([Cl:24])[CH2:22][O:18][C:17](=[O:19])[CH2:16][C:9]1[C:8]2[C:13](=[CH:14][C:5]([O:4][C:1](=[O:3])[CH3:2])=[CH:6][CH:7]=2)[O:12][C:11](=[O:15])[CH:10]=1To a suspension of 7-acetoxycoumarin-4-acetic acid 5 (945 mg, 3.6 mmol, 1 eq) in 47 mL of anhydrous dichloromethane at room temperature under nitrogen was added 2,2,2-trichloroethanol (431 μL, 4.5 mmol, 1.25 eq). A solution of N,N′-dicyclohexylcarbodiimide (818 mg, 4 mmol, 1.1 eq) in 10 mL of anhydrous dichloromethane was added. The reaction mixture was stirred for 15 min, after which it was diluted with dichloromethane and filtered. The filtrate was concentrated under vacuum. Column chromatography on silica gel (CH2Cl2 then CH2Cl2:EtOAc, 10:1) afforded product 6a (1.37 g, 96%): Rƒ 0.78 (CH2Cl2:EtOAc, 5:1); 1H NMR (300 MHz, CDCl3): δ 7.61 (d, 1 H, J5,6 8.7 Hz, H-5), 7.15 (d, 1 H, J6,8 2.1 Hz, H-8), 7.07 (dd, 1 H, J6,8 2.3, J5,6 8.7 Hz, H-6), 6.42 (s, 1 H, H-3), 4.77 (s, 2 H, CH2CCl3), 3.91 (2 s, 2 H, CH2CO2), 2.33 (s, 3 H, OAc); 13C NMR (75 MHz, CDCl3): δ 168.6, 167.0, 154.5, 153.5, 146.5, 125.5, 118.5, 117.0, 116.5, 110.9, 74.6, 37.7, 21.2; ESI-MS: m/z 393 [M+H]+.
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