C[O:2][C:3]1[CH:8]=[CH:7][C:6]([S:9]([N:12]2[C:21]3[CH:22]=[CH:23][S:24][C:20]=3[C:19]3[CH:18]=[CH:17][CH:16]=[CH:15][C:14]=3[CH:13]2[CH3:25])(=[O:11])=[O:10])=[CH:5][CH:4]=1.B(Cl)(Cl)Cl>[I-].C([N+](CCCC)(CCCC)CCCC)CCC.C(Cl)Cl>[CH3:25][CH:13]1[C:14]2[CH:15]=[CH:16][CH:17]=[CH:18][C:19]=2[C:20]2[S:24][CH:23]=[CH:22][C:21]=2[N:12]1[S:9]([C:6]1[CH:7]=[CH:8][C:3]([OH:2])=[CH:4][CH:5]=1)(=[O:11])=[O:10]A solution of 4-[(4-methoxyphenyl)sulfonyl]-5-methyl-4,5-dihydrothieno[3,2-c]isoquinoline (0.45 g, 1.2 mmol) and tetrabutylammonium iodide (1.33 g, 3.6 mmol) in dry methylene chloride (9 mL) was treated dropwise with a solution of boron trichloride in methylene chloride (1.0 M, 3.6 mL, 3.6 mmol) at −78° C. during ca. 5 min. After a further 5 min., the solution was warmed to 23° C. After 16 h the reaction solution was concentrated in vacuo and the residue was taken up in ethyl acetate (25 mL). The organic phase was washed with saturated aqueous sodium bicarbonate (25 mL) and water (10×25 mL), dried (MgSO4), and concentrated in vacuo to give a dark, oily solid (0.68 g) which was suspended in 20% ethyl acetate-hexane and slurried onto a column of silica gel (10 g). Flash chromatography eluting 20-, and then 30% ethyl acetate-hexane gave the product (0.35 g) as a yellow solid. Recrystallization from hot ethyl acetate-hexane gave the title compound (0.28 g, 65%, m.p. 163-65° C.) as shiny white needles.
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