Ethanol → ethyl 3,4-dihydro-6-hydroxy-2H-1-benzopyran-2-carboxylate
Reaktionsgleichung
[OH:1][C:2]1[CH:3]=[CH:4][C:5]2[O:10][CH:9]([C:11]([OH:13])=[O:12])[CH2:8][CH2:7][C:6]=2[CH:14]=1.S(=O)(=O)(O)O.[CH2:20](O)[CH3:21]>>[OH:1][C:2]1[CH:3]=[CH:4][C:5]2[O:10][CH:9]([C:11]([O:13][CH2:20][CH3:21])=[O:12])[CH2:8][CH2:7][C:6]=2[CH:14]=1Komponenten
4
Versuchsvorschrift
A mixture of 60 parts of 3,4-dihydro-6-hydroxy-2H-1-benzopyran-2-carboxylic acid, 800 parts of ethanol and 5.52 parts of concentrate sulfuric acid was stirred for 3 hours at reflux temperature. The reaction mixture was evaporated. Water was added and the product was extracted with trichloromethane. The extract was washed with water, dried, filtered and evaporated. The residue was purified by column chromatography over silica gel using a mixture of trichloromethane and methanol (95:5 by volume) as eluent. The pure fractions were collected and the eluent was evaporated. The residue was solidified in petroleumether. The product was filtered off and dried, yielding 48 parts (70%) of ethyl 3,4-dihydro-6-hydroxy-2H-1-benzopyran-2-carboxylate as a residue (intermediate 21).