Triethyltin bromide → 2-Fluoro-3-triethylstannylbenzofuran

Participants

Reaction Conditions

Reaction Steps

Chloromethyl-4-fluoro-1,4-diazobicyclo[2.2.2]octane bis-(tetrafluoroborate (“Selectfluor®”) (13.11 g, 37.01 mmol) was added to a mixture of benzofuran-2-carboxylic acid (5.0 g, 30.84 mmol) and sodium bicarbonate (6.22 g, 74.0 mmol) stirred in 70 mL of pentane/water (2:5 by volume) at room temperature. After 1 hour at the pentane layer containing 2-fluorobenzofuran was separated from the mixture, and the water layer was extracted with pentane. The combined organic extract was dried through MgSO4, and then the solvent was evaporated to give 2-fluorobenzofuran (1.70 g) as a yellow oil. The 2-fluorobenzofuran (850 mg, 6.24 mmol) and potassium acetate (1.29 g, 13.11 mL) were stirred in of chloroform (3.5 mL) at room temperature, and a solution of bromine (2.05 g, 12.80 mmol) in of chloroform (1 mL), and added slowly into the reaction mixture. After stirring for 1 h at room temperature, the mixture was washed with 5% NaHSO3 then brine, dried through MgSO4, and the solvent was evaporated to give trans-2-fluoro-3-hydro-2,3-dibromo-benzofuran as a light-brown oil (1.70 g). trans-2-Fluoro-3-hydro-2,3-dibromo-benzofuran (1.66 g, 5.62 mmol) was dissolved in anhydrous ethanol (11 mL), and sodium ethoxide (420 mg, 6.18 mmol) was added. The mixture was stirred at RT for 5 min then brine was added, and the solution was extracted with pentane. The pentane layer was washed with water and with brine, dried through MgSO4, and then the solvent was evaporated to give 3-bromo-2-fluorobenzofuran as a light-brown oil (950 mg). Under nitrogen, 3-bromo-2-fluorobenzofuran (465 mg, 2.16 mmol) was dissolved in anhydrous ether (5 mL), and stirred at −78° C. under nitrogen. n-Butyllithium (1.6M, 1.50 mL, 2.38 mmol) was added followed after 5 min by triethylstannyl bromide (680 mg, 2.38 mmol). The mixture was then allowed to warm to room temperature and stirring was continued for a further 1 h. The mixture was quenched, and washed with 1N sodium hydroxide, dried through MgSO4, and then the solvent was evaporated to give the sub-title compound as a brown oil (370 mg), which was used directly without further purification for the next step.

Provenance & Evidence