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The selective silylation of (-)-aristeromycin (I) with Hdms-Cl and imidazole gives the monosilyl ether (II), which is treated with thiocarbonyl dimidazole (TCDI) in hot ethyl acetate to yield the cyclic thiocarbonate (III). The reaction of (III) with 1,3-dimethyl-1,3,2-diazaphospholidine (DMPDP) in refluxing THF affords the desired cyclopentene derivative (IV). In an alternative method, the reaction of (II) with methyl orthoformate provides the cyclic orthoester (V), which undergoes thermal elimination with acetic acid at high temperature giving the desired cyclopentene derivative (IV). The oxidation of (IV) with MCPBA in chloroform yields the N-oxide (VI), which by reaction with Br-CN in methanol affords the oxadiazole derivative (VII). The cleavage of the oxadiazole ring of (VII) and simultaneous methylation with TEA and Me-I provided the cyanoimino derivative (VIII), which is submitted to a Dimroth rearrangement by means of 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) in refluxing aqueous ethanol to give the methoxylated diaminopurine (IX). The reductive cleavage of the methoxyamino group of (IX) with Al/Hg in aqueous THF yields the silylated diaminopurine (X), which is deprotected with HCl in ethanol to afford the free diaminopurine precursor (XI). Finally, this compound is enzymatically deaminated by means of adenosine deaminase to furnish the target (-)-carbovir.