C([O:8][C:9]1[C:17]2[N:16]=[C:15]([NH:18][CH3:19])[N:14]([CH3:20])[C:13]=2[CH:12]=[CH:11][CH:10]=1)C1C=CC=CC=1.[B-](Br)(Br)(Br)[S+](C)C.C(Cl)(Cl)Cl.CO>ClCCl>[OH:8][C:9]1[C:17]2[N:16]=[C:15]([NH:18][CH3:19])[N:14]([CH3:20])[C:13]=2[CH:12]=[CH:11][CH:10]=1To a suspension of 4-benzyloxy-1-methyl-2-methylamino-1H-benzimidazole (150 mg) in dichloromethane (2 ml) was added boron tribromide-methyl sulfide complex (211 mg) in dryice-aceton bath, and the mixture was stirred for 1 hour under ice-cooling and then at ambient temperature overnight. To the reaction mixture were added chloroform-methanol (3:1, v/v) and saturated sodium bicarbonate solution, and insoluble material was filtered off. The separated organic layer was concentrated in vacuo. The residue was purified by preparative thin layer chromatography (chloroform:methanol=8:1, v/v) to give 4-hydroxy-1-methyl-2-methylamino-1H-benzimidazole (49 mg).
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