Synthesis method of key intermediate of ridecevir

The invention provides a novel method for preparing a key intermediate of ridecevir as shown in a formula (VII). Benzyl fully-protected lactone as shown in a formula (I) is used as a starting material and is subjected to ring opening to obtain a compound as shown in a formula (II). The hydroxyl of the compound (II) is protected by a proper protecting group to obtain the compound shown in the formula (III). The compound (III) and the compound (IV) are subjected to coupling, protecting group removal and cyclization to obtain an intermediate shown as a formula (V) by a one-pot method. The intermediate (V) is subjected to two-step conversion to obtain the key intermediate (VII) of the ridecevir. According to the method provided by the invention, the compound (I) which can be bought in the market is used as the starting material, and the key intermediate compound (VII) for preparing the ridecevir is obtained at high yield through five-step reaction, so that the cost is greatly reduced, and the method is suitable f