NOVELTY - An entecavir intermediate is prepared by adding cyclopentane-containing compound in absolute tetrahydrofuran (THF) to obtain cyclopentadiene; reacting cyclopentadiene and sodium 11 (Na11) in THF solution to obtain sodium-containing compound; adding absolute THF and benzyl chloromethyl ether in sodium-containing compound under protection of nitrogen and using potassium iodide as catalyst to obtain o-benzyl containing-compound; and asymmetrically synthesizing carbocyclic substituent group to o-benzyl-containing compound with chiral structure of pinene borane.    USE - Method for preparing entecavir intermediate (claimed).    ADVANTAGE - The method has simple operation and weight yield reaching to 92.3%. It uses tetrabutyl ammonium iodide as phase transfer catalyst, which reduces cost of industrialized production, lessens usage of toxic and harmful solvent and protects environment.    DETAILED DESCRIPTION - Preparing entecavir intermediate comprises:    (A) adding cyclopentane-containing compound of formula (I) in absolute THF to obtain cyclopentadiene (II);    (B) reacting compound (II) and sodium 11 (Na11) in THF solution below 5 degrees C to obtain sodium-containing compound of formula (III);    (C) adding absolute THF and benzyl chloromethyl ether in compound (III) under the protection of nitrogen at - 45 degrees C and using potassium iodide as catalyst to obtain o-benzyl-containing compound of formula (IV);    (D) asymmetrically synthesizing carbocyclic substituent group to compound (IV) with chiral structure of pinene borane as catalyst in 1:1.5 mole ratio at - 35 degrees C to obtain hydroxy-containing compound of formula (V);    (E) dropping mixed solution of hydrogen peroxide and dichloromethane in the mixed solution of compound (V) and diacetone vanadyl, stirring to react for 4-6 hours under protection of nitrogen, reducing to 0 degrees C, a mole ratio of hydrogen peroxide to compound being 1.8:1, using dichloromethane as solvent, adding saturated sodium sulfite solution to separate organic layer, extracting water layer using dichloromethane, and concentrating the compound in vacuum to obtain oxo-containing compound of formula (VI); and    (F) dropping dried potassium carbonate in compound (VI), dropping THF to react at room temperature, adding tetrabutyl ammonium iodide in the system as catalyst, dropping benzyl chloride, stirring to react for 4-6 hours at room temperature, adding alcohol to break hydrogen sodium, decompressing and concentrating, adding water and methyl t-butyl ether in residues to separate out organic phases, extracting water layer using methyl t-butyl ether, combining the organic phases, drying using absolute magnesium sulfate and concentrating to obtain entecavir intermediate compound of formula (VII).