Process for preparing a glucopyranosyl-substituted benzyl-benzene derivative of general formula III, wherein R 1 denotes C 1-3 -alkyl, cyclobutyl, cyclopentyl, cyclohexyl, -tetrahydrofuran-3-yl, -tetrahydrofuran-3-yl or tetrahydropyran-4-yl; and R 2 independently of one another denote hydrogen, (C 1-8 -alkyl)carbonyl, (C 1-8 -alkyl)oxycarbonyl, phenylcarbonyl, phenyl-(C 1-3 -alkyl)-carbonyl, phenyl-C 1-3 -alkyl, allyl, R a R b R c Si, CR a R b OR c, wherein two adjacent groups R 2 may be linked with each other to form a bridging group SiR a R b, CR a R b or CR a OR b -CR a OR b; and R' denotes hydrogen or C 1-6 -alkyl; R a, R b, R c independently of one another denote C 1-4 -alkyl, phenyl or phenyl-C 1-3 -alkyl, while the alkyl groups may be mono- or polysubstituted by halogen; L1 independently of one another are selected from among fluorine, chlorine, bromine, C 1-3 -alkyl, C 1-4 -alkoxy and nitro; while the phenyl groups mentioned in the definition of the above groups may be mono- or polysubstituted with L1; comprising the steps, and:: reacting the organometallic compound of the formula VI wherein R 1 is defined as hereinbefore and M denotes Li, Mg or MgQ, wherein Q denotes Cl, Br, I or an organic moiety; with a gluconolactone of general formula IV wherein R 2 is as hereinbefore defined, in an organic solvent or a mixture of two or more organic solvents; and: adding an aqueous solution comprising one or more acids such that the reaction mixture forms an aqueous phase and an organic phase whereby the organic phase has a pH in the range from 0 to 7; and: separating the organic phase comprising the adduct obtained in the step from the aqueous phase; and: reacting the obtained adduct with water or an alcohol R'-OH, where R' denotes C 1-6 -alkyl, or a mixture thereof in the presence of one or more acids. R 1 denotes C 1-3 -alkyl, cyclobutyl, cyclopentyl, cyclohexyl, -tetrahydrofuran-3-yl, -tetrahydrofuran-3-yl or tetrahydropyran-4-yl; and R 2 independently of one another denote hydrogen, (C 1-8 -alkyl)carbonyl, (C 1-8 -alkyl)oxycarbonyl, phenylcarbonyl, phenyl-(C 1-3 -alkyl)-carbonyl, phenyl-C 1-3 -alkyl, allyl, R a R b R c Si, CR a R b OR c, wherein two adjacent groups R 2 may be linked with each other to form a bridging group SiR a R b, CR a R b or CR a OR b -CR a OR b; and R' denotes hydrogen or C 1-6 -alkyl; R a, R b, R c independently of one another denote C 1-4 -alkyl, phenyl or phenyl-C 1-3 -alkyl, while the alkyl groups may be mono- or polysubstituted by halogen; L1 independently of one another are selected from among fluorine, chlorine, bromine, C 1-3 -alkyl, C 1-4 -alkoxy and nitro;: reacting the organometallic compound of the formula VI wherein R 1 is defined as hereinbefore and M denotes Li, Mg or MgQ, wherein Q denotes Cl, Br, I or an organic moiety; with a gluconolactone of general formula IV wherein R 2 is as hereinbefore defined, in an organic solvent or a mixture of two or more organic solvents; and: adding an aqueous solution comprising one or more acids such that the reaction mixture forms an aqueous phase and an organic phase whereby the organic phase has a pH in the range from 0 to 7; and: separating the organic phase comprising the adduct obtained in the step from the aqueous phase; and: reacting the obtained adduct with water or an alcohol R'-OH, where R' denotes C 1-6 -alkyl, or a mixture thereof in the presence of one or more acids.