Synthesis method of lamivudine intermediate

The invention discloses a synthetic method of lamivudine intermediate, namely (2R, 5S)-5-(5-cytosine-1-base)-1, 3-oxathiolane-2- carboxylic acid-L-menthyl ester with the structural formula shown as the formula (VI). (2R, 5S)-5- hydroxyl-1, 3- oxathiolane -2- carboxylic acid-L-menthyl ester with the structural formula shown as the formula (III) is taken as raw material and a chlorine substitute with the structural formula shown as the formula (IV) is obtained by chloro-substituted reaction; the chlorine substitute (IV) and N, O-bi (tri-silicon-base) 5-cytosine with the structural formula shown as the formula (V) are condensed and hydrolyzed to obtain the intermediate. The method takes bi (trichloromethyl) carbonate to replace thionyl chloride applied in the prior art as a chloro-substituted reagent and has the advantages of safe and reliable operation and environmental protection.