Example 4: Preparation of 2,4,5-tribromo-1-ethoxymethylpyrrole-3-carbonitrile (STR7)
1. a dispersion of 60% NaH in mineral oil (1.22 g, 0.0304 mol NaH) was stirred into suspension in dry tetrahydrofuran.
2. A tetrahydrofuran solution of 2,4,5-tribromopyrrole-3-carbonitrile (10.0 g, 0.0304 mol) was added dropwise at 20 °C to 30 °C. The dropwise addition process lasted for 20 min.
3. After completion of the dropwise addition, stirring was continued at ambient temperature for 30 minutes.
4. Bromochloromethane (11.80 g, 0.0912 mol) and solid sodium ethoxide (6.2 g, 0.0912 mol) were added to the reaction mixture.
5. The reaction mixture was heated to reflux temperature and held for 4 hours.
6. After completion of the reaction, it was cooled to room temperature and concentrated in vacuum to remove the solvent.
7. The residue was diluted with water and ethyl acetate and the organic phase was separated. 8.
8. The organic phase was washed with water and brine and dried over anhydrous sodium sulfate. 9.
9. After filtration, the organic phase was concentrated in vacuum to obtain the crude product. 10.
10. The crude product was purified by fast chromatography (silica gel; ethyl acetate/heptane as eluent) to give 3-cyanopyrrole as a white solid (5.4 g, 46.7% yield) with a melting point of 139 °C to 143 °C. The residue was diluted with water and ethyl acetate.
