[CH3:1][C:2]1[C:11]2[C:6](=[C:7]([CH3:13])[C:8]([OH:12])=[CH:9][CH:10]=2)[O:5][C:4](=[O:14])[CH:3]=1.Br[CH2:16][CH:17]=[CH2:18].C(=O)([O-])[O-].[K+].[K+]>CC(C)=O>[CH3:1][C:2]1[C:11]2[C:6](=[C:7]([CH3:13])[C:8]([O:12][CH2:18][CH:17]=[CH2:16])=[CH:9][CH:10]=2)[O:5][C:4](=[O:14])[CH:3]=1A solution of 4,8-dimethyl-7-hydroxycoumarin (4.85 g, 25.5 mmoles) in 200 ml of acetone was reacted with 3-bromopropene (4.62 g, 38.2 mmoles) in the presence of anhydrous potassium carbonate (10 g). The reaction mixture was heated under reflux for 4 hours, cooled and filtered. The collected solid was washed with fresh acetone. The filtrate and washings were combined and the solvent evaporated under reduced pressure. The crude product was recrystallized from methanol to yield the title compound as fluffy, white needles, m.p. 107°-108° C., 3.5 g, 60% yield. 1H NMR: 2.3 (s, 3H, C8 --CH3), 2.4 (d, 3H, C4 --CH3J=1.2 Hz), 4.6 (dt, 2H, O--CH2J=1.5, 4.8 Hz), 5.4 (m, 2H, =CH2J=4.8 Hz), 5.9 (m, 1H, --CH=CH2), 6.1 (d, 1H, C3 --H, J=1.2 Hz), 6.8 (d, 1H, C6 --H, J=9.0 Hz), 7.3 (d, 1H, C5 --H, J=9.0 Hz)
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