Boron tribromide → 1-(4-Benzo[b]thiophen-2-yl-benzyl)-1,2,3,4-tetrahydro-isoquinoline-6,7-diol hydrobromide

1-(4-Benzo[b]thiophen-2-yl-benzyl)-1,2,3,4-tetrahydro-isoquinoline-6,7-diol hydrobromide (22) was prepared as follows: To a stirred solution of 0.15 g (0.29 mmole) of 1-(4-benzo[b]thiophen-2-yl-benzyl)-6,7-dimethoxy-8-methyl-3,4-dihydro-1-H-isoquinoline-2-carboxylic acid tert-butyl ester in 10 ml of anhydrous dichloromethane under argon at −70° C., 0.9 ml (3 mol. equiv.) of 1M boron tribromide solution in n-hexanes was added. The stirred mixture was allowed to reach room temperature overnight and the solvents were evaporated under reduced pressure. The residue was dissolved in 10 ml of methanol and, again, the solvent was evaporated under reduced pressure. The solid residue was mixed with 10 ml of ether, separated on a glass filter funnel, washed with ether (3×20 ml) to afford an off-white solid, 130 mg (91%), mp 251-254° C.