Preparation method of apremilast intermediate

The invention discloses a preparation method of an apremilast intermediate, which comprises the following steps: by taking (R)-1-(3-ethoxy-4-methoxyphenyl)-2-(methylsulfonyl) ethylamine as a raw material, anhydrous cupric sulfate as a catalyst and potassium permanganate as an oxidizing agent, carrying out primary amine oxidation to obtain imine under the protection of ammonia gas or an ammonia-containing solvent, and then carrying out primary amine oxidation to obtain the apremilast intermediate by taking sodium borohydride as a reducing agent. N-acetyl-L-leucine is used for resolution, methanol is used for refining, the process reaction temperature is not high or low, pressurization is avoided, few impurities are generated in the reaction, the impurities are controllable, the yield in each step is high, and the purity is good; according to the present invention, the unused (R)-1-(3-ethoxy-4-methoxyphenyl)-2-(methylsulfonyl) ethylamine is converted into the apremilast key chiral intermediate (S)-1-(3-ethoxy-4