General procedure: 4-Hydroxybenzaldehyde (1 eq.) is dissolved in acetone. Potassium carbonate (4.5 eq.) dissolved in water was added slowly and the reaction mixture was stirred at room temperature for 10 minutes. Subsequently, 1,3-dibromopropane (0.5 eq.) dissolved in acetone was added dropwise. The reaction mixture was continued to be stirred for 4 hours. The progress of the reaction was monitored by thin layer chromatography (TLC) and after confirming the completion of the reaction, the solvent was removed by evaporation under reduced pressure to give the crude product. The crude product was washed with water, filtered and recrystallized from ethanol-water mixed solvent to give 4,4'-(propane-1,3-diylbis(oxy))dibenzaldehyde (13). Yield: 92%, melting point: 179.6-180.5 °C. 1H-NMR (DMSO-d6, 200 MHz, Me4Si) δ (ppm): 2.21 (t, 2H, -CH2-propylidene-bridged), 4.22 (s, 4H, -O-CH2-), 7.10 (d, J = 8.6 Hz, 4H, aryl proton, H-3, H-5), 7.82 (d, J = 8.6 Hz, 4H, aromatic proton, H-2, H-6), 9.82 (s, 2H, -CHO).13C-NMR (50 MHz, DMSO-d6, Me4Si) δ: 28.7 (C-2'), 85.2 (C-1'), 115.3 (C-3, C-5), 130.1 (C-4), 132.2 (C-2, C-5), 132.2 (C-4), 132.2 (C-4), 132.2 (C-4), 132.2 (C-4), 132.2 (C-4), 132.2 (C-4), 132.2 (C-4) 132.2 (C-2, C-6), 163.8 (C-1), 191.6 (-CHO).MS/FAB+: m/z 285 (M + H+). (calculated value C17H16O4H+ 285.31).
