[OH:1][C:2]1[CH:3]=[CH:4][C:5]2[O:10][CH:9]([C:11]([O:13][CH2:14][CH3:15])=[O:12])[CH2:8][CH2:7][C:6]=2[CH:16]=1.[H-].[Na+].Br[CH2:20][CH:21]=[CH2:22]>CN(C)C=O>[CH2:22]([O:1][C:2]1[CH:3]=[CH:4][C:5]2[O:10][CH:9]([C:11]([O:13][CH2:14][CH3:15])=[O:12])[CH2:8][CH2:7][C:6]=2[CH:16]=1)[CH:21]=[CH2:20]To a stirred mixture of 40 parts of ethyl 3,4-dihydro-6-hydroxy-2H-1-benzopyran-2-carboxylate and 360 parts of N,N-dimethylformamide were added portionwise 8.6 parts of a sodium hydride dispersion 50% (foaming). After stirring for 30 minutes, a solution of 21.7 parts of 3-bromo-1-propene in 18 parts of N,N-dimethylformamide was added dropwise. Upon completion, the whole was heated to about 70° C. and stirring was continued for 22 hours at 70° C. The reaction mixture was evaporated and the residue was taken up in water. The product was extracted with 1,1'-oxybisethane. The extract was washed with a sodium chloride solution 10%, dried, filtered and evaporated. The oily residue was purified by column chromatography over silica gel using trichloromethane as eluent. The pure fractions were collected and the eluent was evaporated, yielding 33.6 parts (70.2%) of ethyl 3,4-dihydro-6-(2-propenyloxy)-2H-1-benzopyran-2-carboxylate as a residue (intermediate 28).
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