Preparation method of alvimopan

The invention provides a preparation method of alvimopan and an intermediate for synthesizing the alvimopan. The preparation method comprises the following steps of: designing a process route through a two-chain method, respectively synthesizing initial raw materials, then condensing and hydrolyzing to obtain the alvimopan. The method can be used for directionally synthesizing a single optical isomer through N-alkylation reaction under an alkaline condition, the configuration change of the chiral centers of the raw materials and the product can not be generated both in reaction conditions anda post-processing method, and the obtained product can be hydrolyzed into the alvimopan under the mild alkaline condition.