[OH:1][C:2]1[CH:3]=[C:4]([CH:8]=[CH:9][C:10]=1[OH:11])[C:5]([OH:7])=[O:6].C([O-])([O-])=O.[K+].[K+].[CH2:18](Br)[CH2:19][CH3:20]>CN(C=O)C.CCOC(C)=O>[CH2:18]([O:1][C:2]1[CH:3]=[C:4]([CH:8]=[CH:9][C:10]=1[O:11][CH2:5][CH2:4][CH3:8])[C:5]([O:7][CH2:10][CH2:2][CH3:3])=[O:6])[CH2:19][CH3:20]A mixture of 3,4-dihydroxybenzoic acid (0.65 g; 4.22 mmol), anhydrous K2CO3 (1.75 g; 12.7 mmol) and n-PrBr (1.5 ml; 4 mmol) in anhydrous DMF (5 ml) was stirred at ˜55° C. overnight. After cooling to room temperature, the mixture was diluted to 25 ml with EtOAc, washed with H2O (2×10 ml), brine, dried over anhydrous MgSO4, filtered and the filtrate evaporated to dryness to give the title compound (0.94 g; 80%), as heavy syrup, which was used in next step without further purification. 1H-NMR (CDCl3) 0.97-1.04 (m, 9H); 1.7-1.9 (m, 6H); 3.97-4.02 (m, 4H); 4.2-4.26 (m, 2H); 6.85 (d, 1H, J=8.4 Hz); 7.53 (s, 1H); 7.62 (d, 1H, J=8.4 Hz).
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