1,2-Dibromoethane → 1-[5-Bromo-2-(2-bromoethoxy)phenyl]ethanone

Beteiligte Stoffe

Reaktionsschritte

To a stirred solution of 5-bromo-2-hydroxyacetophenone (15.29 g; 71 mmol) in 2-butanone (150 ml) was added K2CO3 (21 g; 152 mmol) then 1,2-dibromoethane (30 ml; 350 mmol). The reaction mixture was heated at reflux temperature overnight (17 h), cooled, filtered (acetone washing) and the solvent evaporated. The residue was treated with a mixture of Et2O/EtOAc (4:1; 250 ml) and the resulting solid removed by filtration. The filtrate was washed with 2M NaOH (150 ml), dried (MgSO4) and concentrated to give 1-[5-bromo-2-(2-bromo-ethoxy)-phenyl]-ethanone as an off-white crystalline solid (15.99 g). This solid was dissolved in anhydrous THF (300 ml), cooled to 0° C. and treated with NaH (2.11 g of a 60 wt % suspension in mineral oil; 53 mmol). The reaction mixture was carefully heated to reflux and heating continued overnight (17 h). The reaction mixture was cooled, quenched with 2M HCl (50 ml) and partitioned between brine (300 ml) and EtOAc (200 ml). The organic layer was dried (MgSO4), concentrated and purified by ISCO (hexanes/EtOAc) to give 7-bromo-3,4-dihydro-2H-benzo[b]oxepin-5-one as a pale yellow oil (9.84 g; 57%). δH (400 MHz, CDCl3) 2.24 (quintet, J=6.8, 2H), 2.91 (t, J=6.8, 2H), 4.25 (t, J=6.8, 2H), 6.98 (d, J=8.8, 1H), 7.52 (dd, J=8.8 and 2.8, 1H), 7.90 (d, J=2.8, 1H).

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