a) Synthesis of 5-(benzyloxy)-1H-indole-3-carbaldehyde: Phosphoryl chloride (1.5 g, 9.9 mmol) was slowly added dropwise to 15 mL of N,N-dimethylformamide (DMF) cooled in an ice bath under stirring conditions. After removing the ice bath, the reaction was continued with stirring for 15 min. Subsequently, 5-benzyloxyindole (2.00 g, 8.96 mmol) was added and the reaction mixture was heated to 50-60 °C and maintained at this temperature for 1.5 hours. After completion of the reaction, the mixture was poured into ice water and adjusted to alkaline with 2 M sodium hydroxide solution. The mixture was refluxed for 2 minutes, cooled and filtered to collect the solid product. The solid was washed with water and dried to give the target compound 5-(benzyloxy)-1H-indole-3-carboxaldehyde in a yield of 1.88 g (84% yield). The product was characterized by 1H NMR (400 MHz, DMSO-d6) with the following chemical shifts: δ 5.88 (s, 1H), 8.20 (s, 1H), 7.68 (d, 1H), 7.50-7.25 (m, 6H), 6.96 (dd, 1H), 5.11 (s, 2H), 4.02 (s, 1H).
