Method for preparing substituted indole-3-methanal compound

The invention relates to the field of organic synthesis and medical intermediate preparation and especially relates to a method for preparing a substituted indole-3-methanal compound. The method comprises the following steps that N,N-dimethylformamidodimethylacetal or N,N-methylformamidodiethylacetal and substituted 2-nitrotoluene undergo a reflux reaction to produce beta-dimethylamino-2-nitrostyrene; beta-dimethylamino-2-nitrostyrene and a mixed solution of hydrazine and alcohol undergo a reaction to produce a substituted indole; and the substituted indole, dimethylformamide (DMF) and phosphorus oxyhalogen undergo a reaction to produce the substituted indole-3-methanal compound. Yields of all processes of the method provided by the invention are more than 90%. A total yield of the method is more than 80%.