NOVELTY - Preparing anti-hepatitis B virus drug entecavir (2-amino-9-((1S,3S,4S)-4-hydroxy-3-hydroxymethyl-2-methylidenecyclopentyl)-1,9-dihydro-6H-purin-6-one), comprises e.g. reacting ((1R,2S,3S,5R)-3-(1-phenylsilolan-1-yl)-6-oxabicyclo(3.1.0)hexane-1,2-diyl)dimethanol compounds (I) with 6-o-benzylguanine, carrying out Eastwood deoxygenation of obtained compound to obtain ((1R,3S,5S)-3-(2-amino-6-(benzyloxy)-9H-purin-9-yl)-2-methylene-5-(1-phenylsilolan-1-yl)cyclopentyl)methanol compounds (III), then removing benzyl group of (III), and carrying out protodesilylation and oxidation respectively.    USE - The method is useful for preparing anti-hepatitis B virus drug entecavir.    ADVANTAGE - The method: utilizes raw material having silane ring structure, which increases rigidity of molecule, and thus it ensures easy crystallization and purification of produced product; produces less tar during reaction; has high product yield; and is suitable for industrial production.    DETAILED DESCRIPTION - Preparing anti-hepatitis B virus drug entecavir (2-amino-9-((1S,3S,4S)-4-hydroxy-3-hydroxymethyl-2-methylidenecyclopentyl)-1,9-dihydro-6H-purin-6-one), comprises (i) reacting ((1R,2S,3S,5R)-3-(1-phenylsilolan-1-yl)-6-oxabicyclo(3.1.0)hexane-1,2-diyl)dimethanol compounds of formula (I) with 6-o-benzylguanine under catalysis of an alkali to obtain ((1S,2S,3S,5S)-5-(2-amino-6-(benzyloxy)-9H-purin-9-yl)-1-hydroxy-3-(1-phenylsilolan-1-yl)cyclopentane-1,2-diyl)dimethanol compounds of formula (II), (ii) carrying out Eastwood deoxygenation of (II) with an ester reagent to obtain ((1R,3S,5S)-3-(2-amino-6-(benzyloxy)-9H-purin-9-yl)-2-methylene-5-(1-phenylsilolan-1-yl)cyclopentyl)methanol compounds of formula (III), and then removing benzyl group of (III) in presence of an acid to obtain 2-amino-9-((1S,3R,4S)-3-(hydroxymethyl)-2-methylene-4-(1-phenylsilolan-1-yl)cyclopentyl)-1H-purin-6(9H)-one compounds of formula (IV), and (iii) carrying out protodesilylation reaction of (IV) with an acid reagent, and then carrying out oxidation with hydrogen peroxide/potassium bicarbonate/potassium fluoride to obtain final product.    n = 0-2.