Boron tribromide → 5-Hydroxy-2,3-dihydrobenzofuran-6-carbaldehyde
Reaction equation
C[O:2][C:3]1[C:4]([CH:12]=[O:13])=[CH:5][C:6]2[O:10][CH2:9][CH2:8][C:7]=2[CH:11]=1.B(Br)(Br)Br>C(Cl)Cl>[OH:2][C:3]1[C:4]([CH:12]=[O:13])=[CH:5][C:6]2[O:10][CH2:9][CH2:8][C:7]=2[CH:11]=1Participants
4
Reactant 2
Product 1
Reagents, catalysts & solvents 1
Procedure
A solution of 5-methoxy-2,3-dihydrobenzofuran-6-carboxaldehyde (24.00 g, 135 mmol) in dry methylene chloride (800 mL) under nitrogen was cooled to an internal temperature of -67°. A solution of boron tribromide (1M in methylene chloride, 63.0 mL 63.0 mmol) was added dropwise. The cooling bath was removed and the mixture allowed to stir for 2.5 hours. The reaction was then quenched by the dropwise addition of methanol (25 mL) and the resulting mixture poured into 10% aqueous sodium chloride (100 mL). The layers were separated and the aqueous layer washed with methylene chloride (2×250 mL), and the combined organic extracts washed with 10% sodium chloride (2×500 mL), dried (Na2SO4), and concentrated. Purification by preparative HPLC (Waters Prep 500, 9:1 hexane:ethyl acetate as eluant) afforded 5-hydroxy-2,3-dihydrobenzofuran-6-carboxaldehyde (16.82 g, 76.1%), m.p. 102-104° C.