A production method for producing a compound represented by the general formula or a salt thereof, comprising reacting a trimethylsilylated compound with a compound represented by the general formula: or a salt thereof, in the presence of a Lewis acid catalyst, to obtain the compound represented by the general formula or a salt thereof, wherein: - said trimethylsilylated compound is a compound obtained by reaction of a compound represented by the general formula (IVb): with a trimethylsilylating agent; - R 4, R 5, and R 6 are the same or different and each represents a hydrogen atom, a hydroxy group, a protected hydroxy group, an alkoxy group having 1 to 4 carbon atoms, a mercapto group, a protected mercapto group, an alkylthio group having 1 to 4 carbon atoms, an amino group, a protected amino group, an amino group substituted by (an) alkyl group(s) having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a halogen atom; - wherein X and Y are the same or different and each represents a protective group for the hydroxy group; - wherein Z represents a protective group for the hydroxy group that is an aliphatic acyl group; an aromatic acyl group; a tetrahydropyranyl or tetrahydrothiopyranyl group; a tetrahydrofuranyl or tetrahydrothiofuranyl group; a lower alkoxymethyl group; a lower alkoxylated lower alkoxymethyl group; a halogeno-lower alkoxymethyl group; a lower alkoxylated ethyl group; a halogenated ethyl group; a methyl group substituted by 1 to 3 aryl groups; a methyl group substituted by 1 to 3 aryl groups with the aryl ring substituted by lower alkyl, lower alkoxy, halogen or a cyano group; a lower alkoxycarbonyl group; a halogen-substituted lower alkoxycarbonyl group; an alkenyloxycarbonyl group; or an aralkyloxycarbonyl group with the aryl ring optionally substituted by 1 or 2 lower alkoxy or nitro groups; - A is a methylene group; - R represents a silyl protective group; and - B represents a purin-9-yl group or a substituted purin-9-yl group having (a) substituent(s) selected from group α, wherein the group α is a group consisting of a hydroxy group, a protected hydroxy group, an alkoxy group having 1 to 4 carbon atoms, a mercapto group, a protected mercapto group, an alkylthio group having 1 to 4 carbon atoms, an amino group, a protected amino group, an amino group substituted by (an) alkyl group(s) having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, and a halogen atom. - said trimethylsilylated compound is a compound obtained by reaction of a compound represented by the general formula (IVb): with a trimethylsilylating agent; - R 4, R 5, and R 6 are the same or different and each represents a hydrogen atom, a hydroxy group, a protected hydroxy group, an alkoxy group having 1 to 4 carbon atoms, a mercapto group, a protected mercapto group, an alkylthio group having 1 to 4 carbon atoms, an amino group, a protected amino group, an amino group substituted by (an) alkyl group(s) having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a halogen atom; - wherein X and Y are the same or different and each represents a protective group for the hydroxy group; - wherein Z represents a protective group for the hydroxy group that is an aliphatic acyl group; an aromatic acyl group; a tetrahydropyranyl or tetrahydrothiopyranyl group; a tetrahydrofuranyl or tetrahydrothiofuranyl group; a lower alkoxymethyl group; a lower alkoxylated lower alkoxymethyl group; a halogeno-lower alkoxymethyl group; a lower alkoxylated ethyl group; a halogenated ethyl group; a methyl group substituted by 1 to 3 aryl groups; a methyl group substituted by 1 to 3 aryl groups with the aryl ring substituted by lower alkyl, lower alkoxy, halogen or a cyano group; a lower alkoxycarbonyl group; a halogen-substituted lower alkoxycarbonyl group; an alkenyloxycarbonyl group; or an aralkyloxycarbonyl group with the aryl ring optionally substituted by 1 or 2 lower alkoxy or nitro groups; - A is a methylene group; - R represents a silyl protective group; and - B represents a purin-9-yl group or a substituted purin-9-yl group having (a) substituent(s) selected from group α, wherein the group α is a group consisting of a hydroxy group, a protected hydroxy group, an alkoxy group having 1 to 4 carbon atoms, a mercapto group, a protected mercapto group, an alkylthio group having 1 to 4 carbon atoms, an amino group, a protected amino group, an amino group substituted by (an) alkyl group(s) having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, and a halogen atom.