General steps:
1. Bromination reaction: To a stirred acetonitrile solution of 1,2,3,4-tetrahydroquinoline (20.0 g, 150 mmol, 1.0 eq.) was added N-bromosuccinimide (25.5 g, 143 mmol, 0.95 eq.) in 4 portions at 0°C, each 20 minutes apart. The reaction mixture was continued to be stirred for 3 h at 0 °C.
2. Reaction monitoring: the progress of the reaction was monitored by thin layer chromatography (TLC), the unfolding agent was 10% ethyl acetate-hexane and the product Rf value was 0.55.
3. Post-treatment: After completion of the reaction, the organic layer was diluted with the addition of ether and washed sequentially with saturated sodium bicarbonate solution, water and brine. The organic phase was dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure.
4. Purification: The crude product was purified by column chromatography on silica gel (100-200 mesh) with hexane solution of 5% ethyl acetate as eluent to give 6-bromo-1,2,3,4-tetrahydroquinoline (20.0 g, 64% yield) as a yellow oil.
5. Characterization of the product: Liquid chromatography-mass spectrometry (LCMS) analysis showed a purity of 92.25% (ES+): m/z 212.0 (M+H+); retention time (tr) = 2.06 min.
