[CH2:1]1[C:6]2[CH:7]=[CH:8][CH:9]=[CH:10][C:5]=2[CH2:4][C:3](=[O:11])[O:2]1.[H-].[Al+3].[H-].[H-].CCOCC.Cl>ClCCl>[CH2:1]1[C:6]2[CH:7]=[CH:8][CH:9]=[CH:10][C:5]=2[CH2:4][CH:3]([OH:11])[O:2]1To a solution of 3.00 g (0.020 mol) of 1,4-dihydro-3H-2-benzopyran-3-one in 100 mL of dry dichloromethane, cooled to -78° C., was added dropwise, over 1 hour, 24 mL (0.022 mol) of a 1M solution of disobutyl aluminum hydride in dichloromethane. After stirring at -78° C. for 2 hours and at 0° C. for 15 minutes, 100 mL of ether was added, followed by dropwise addition of 1.2N HCl until a PH of 1-2 was reached. Separation of the organic phase, extraction of the aqueous phase with ether and concentration of the combined dried (MgSO4) extracts provided 2.8 g (91%) of 3,4-dihydro-1H-2-benzopyran-3- ol. This product decomposes on standing or on chromatography on silica gel and consequently was used directly for the next reaction step. TLC Rf 0.13 (SiO2, CH2Cl2, brown-orange CAS and heat).
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