Sulfuric Acid → 2-Bromo-5H-pyrrolo[2,3-b]pyrazine-7-carbaldehyde

Participants

Reaction Steps

A stock solution of Jones reagent (2.67 M) was prepared by carefully adding concentrated H2SO4 (2.3 mL) to CrO3 (2.67 g) then diluting to 10 mL with H2O. To a partial suspension of (2-bromo-5H-pyrrolo[2,3-b]pyrazin-7-yl)-methanol (4.6 g, 20.1 mmol) in acetone (300 mL) was slowly added Jones reagent (9 mL, 24.0 mmol). During the addition the starting material gradually dissolved and a thick green precipitate was formed. The reaction mixture was stirred for 15 min then quenched with i-PrOH (2 mL) and filtered over Celite, rinsing with acetone. The filtrate was concentrated to provide 4.76 g of 2-bromo-5H-pyrrolo[2,3-b]pyrazine-7-carbaldehyde as a yellow-orange solid that was used without further purification. To a solution of this solid in DMF (50 mL) at 0° C. was added NaH (60% in mineral oil, 1.2 g, 30.1 mmol). The reaction mixture was stirred at room temperature for 30 min then cooled back to 0° C. and 2-(trimethylsilyl)ethoxymethyl chloride (4.3 mL, 24.1 mmol) was slowly added. The reaction mixture was warmed to room temperature and stirred for 1 h then quenched with H2O and extracted with EtOAc (3×). The combined organics were washed with H2O (3×) and brine then dried over MgSO4 and concentrated. The residue was purified by SiO2 chromatography (20% to 30% EtOAc/hexanes) to isolate 3.82 g (53%) of 2-bromo-5-(2-trimethylsilanyl-ethoxymethyl)-5H-pyrrolo[2,3-b]pyrazine-7-carbaldehyde as a yellow solid.

Provenance & Evidence