General procedure for the synthesis of 2-(4-bromobutoxy)tetrahydro-2H-pyran from 3,4-dihydro-2H-pyran and 4-bromo-1-butanol: 3,4-dihydro-2H-pyran (8.0 g, 95.36 mmol) was slowly added to a solution of 4-bromo-1-butanol (12.0 g, 79.47 mmol) in dichloromethane (150 mL) at 0 °C , followed by the addition of p-toluenesulfonic acid (20 mg) as a catalyst. After 1 hour of reaction, the reaction was carefully quenched with saturated NaHCO3 solution (5 mL), followed by washing the organic layer with water (100 mL) and brine (70 mL) sequentially. The organic layer was concentrated in vacuum to give the crude product. The residue was purified by silica gel column chromatography using 2% ethyl acetate/hexane as eluent to afford 2-(4-bromobutoxy)tetrahydro-2H-pyran (16.57 g, 88% yield) as a colorless oil. Thin layer chromatography (TLC) analytical conditions: 10% ethyl acetate/hexane, Rf value 0.50. 1H NMR (CDCl3, 300MHz) δ 4.58 (t, J = 2.5Hz, 1H), 3.90-3.72 (m, 2H), 3.38-3.50 (m, 4H), 1.92-2.04 (m, 2H), 1.65-1.80 ( m, 4H), 1.50-1.60 (m, 4H).
