Preparation method of uconafil intermediate

The invention relates to the technical field of drug synthesis, and provides a preparation method of a compound shown as a formula (III), an ukekadafil intermediate 2-amino-4-methyl-1-propyl-1H-pyrrole-3-formonitrile and hydrochloride thereof (shown as a formula VI), and the preparation method of the compound shown as the formula (III) comprises the following steps: (1) reacting halogenated ethyl acetate with n-propylamine to obtain a compound shown as a formula (I); (2) reacting the compound in the formula (I) in the presence of a first alkaline substance to obtain a compound in a formula (II); and (3) reacting the compound shown in the formula (II) with acetic anhydride in the presence of a second alkaline substance to obtain a compound shown in a formula (III). According to the preparation method, the adopted raw materials are cheap and easy to obtain, the production cost is low, toxic or explosive reagents with large harm do not need to be adopted, the production process is safe and controllable, and indu