[OH:1][C:2]1[C:11]2[S:10][CH2:9][CH2:8][CH2:7][C:6]=2[CH:5]=[CH:4][CH:3]=1.[OH-].[Na+].[Br:14][CH:15](Br)[CH3:16]>[Br-].C([N+](CCCC)(CCCC)CCCC)CCC.C(#N)C>[Br:14][CH2:15][CH2:16][O:1][C:2]1[C:11]2[S:10][CH2:9][CH2:8][CH2:7][C:6]=2[CH:5]=[CH:4][CH:3]=1Tetrabutylammonium bromide (1.94 g 6 mmol; 0.2 eq.), phase-transfer agent, is added to a heterogeneous mixture composed of 8-hydroxy-3,4-dihydro-2H-1-benzothiopyran (5 g; 30 mmol), acetonitrile (30 ml) and a 1.6N sodium hydroxide solution (28.3 ml; 45 mmol; 1.5 eq.). Dibromoethane (10 ml; 60 mmol; 1.5 eq.) is added after 30 minutes' stirring, the stirring being continued for 24 hours at 30° C. Concentration of the various phases under reduced pressure at 25° C. is followed by extraction of the products with dichloromethane. Washing with a 5% sodium hydroxide solution allows a first purification, which is followed by purification over a silica column eluted with a 3:7 AcOEt/PE mixture, yielding the brominated title compound.
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