NOVELTY - A tert-butyl (3R,6S)-6-(2-(3-fluoro-6-methoxy-1,5-naphthyridin-4-yl)acetyl)tetrahydro-2H-pyran-3-ylcarbamate (I) is new.    USE - For the stereoselective preparation of tert-butyl (3R,6S)-6-((S)-2-(3-fluoro-6-methoxy-1,5-naphthyridin-4-yl)-1-hydroxyethyl)tetrahydro-2H-pyran-3-ylcarbamate; (S)-1-((2S,5R)-5-aminotetrahydro-2H-pyran-2-yl)-2-(3-fluoro-6-methoxy-1,5-naphthyridin-4-yl)ethanol (claimed); and for manufacturing antibiotics.    ADVANTAGE - The compound (I) is cheap, more efficient and environment-friendly.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) preparation of the compound (I);    (2) use of tert-butyl (3R,6S)-6-(methoxy(methyl)carbamoyl)tetrahydro-2H-pyran-3-ylcarbamate (Ib) for the stereoselective preparation of tert-butyl (3R,6S)-6-((S)-2-(3-fluoro-6-methoxy-1,5-naphthyridin-4-yl)-1-hydroxyethyl)tetrahydro-2H-pyran-3-ylcarbamate (Ic), involving reacting, in a polar aprotic solvent or a polar aprotic solvent mixture, the compound (Ib) either with diisobutylaluminum hydride (DIBAH), or with triisopropoxyaluminum, dimethylaluminum chloride or diethylaluminum chloride in the presence of isopropyl alcohol (iPrOH);    (3) use of the compound (I) in a process for the stereoselective preparation of (S)-1-((2S,5R)-5-aminotetrahydro-2H-pyran-2-yl)-2-(3-fluoro-6-methoxy-1,5-naphthyridin-4-yl)ethanol (Id), involving: reacting the compound (I), in a polar aprotic solvent or solvent mixture, either with DIBAH, or with triisopropoxyaluminum or dimethylaluminum chloride in the presence of iPrOH, affording the compound (Ic); and deprotecting, in acidic conditions, the compound (Ic), affording the compound (Id); and    (4) stereoselective preparation of a compound of formula (II), involving: reacting, in a polar aprotic solvent or a polar aprotic mixture of solvents, a compound of formula (I'), either with DIBAH, or with triisopropoxyaluminum, dimethylaluminum chloride or diethylaluminum chloride in the presence of iPrOH.    R1=H or -CO-R2;    R'1=H or -CO-R'2;    R2=trifluoromethyl, tert-butoxy, benzyloxy or 4-methoxybenzyloxy;    R'2=tert-butoxy, benzyloxy or 4-methoxybenzyloxy.