Process for preparing [IR-(1.alpha.,2.beta.-3.alpha.)]-2-amino-9-[2,3-bis(hydroxymethyl)cyclob utyl]-1,9-dihydro-6H-purin-6-one

A process for preparing the antiviral agent [1R-(1.alpha., 2.beta., 3.alpha.])-2-amino-9-[2,3-bis(hydroxymethyl)cyclobutyl ]-1,9-dihydro-6H-purin-6-one which comprises

• a) treating an optically active compound of the formula ##STR19## with a reducing agent selected from the group consisting of dialkylaluminum chlorides, alkylaluminum dichlorides, trialkylaluminum compounds, diphenylsilane in the presence of tris(triphenylphosphine) rhodium (I) chloride, and iridium tetrachloride in the presence of phosphorous acid wherein alkyl is straight or branched chain of 1 to 20 carbons;
• Prot is a hydroxy protecting group selected from the group consisting of benzyl, substituted benzyl, ##STR20## t-butyldimethylsilyl, t-butyldiphenylsilyl, (triphenylmethyl) dimethylsilyl, methyldiisopropylsilyl, and triisopropylsilyl, and R.sub.1 is straight or branched chain lower alkyl of 1 to 6 carbons or phenyl provided that when the reducing agent is a trialkylaluminum compound Prot cannot be ##STR21## to give the optically active compound of the formula ##STR22## b) treating the product of step (a) with tosyl chloride to give the optically active compound of the formula ##STR23## c) treating the product of step (b) with the benzyloxyguanine compound of the formula ##STR24## to give the optically active compound of the formula ##STR25## and d) treating the product of step (c) to remove the protecting groups and yield the desired antiviral agent.