A dry 3 L, 4-necked flask equipped with a mechanical stirrer, thermometer, addition funnel and refluxing condenser is charged with 50 g 8-(phenylmethoxy)-5-(α-chloroacetyl)-(1H)-quinolin-2-one and 600 mL dry THF under N2. Then 15 mL of a 1 molar solution of (R)-tetrahydro-1-methyl-3,3-diphenyl-(1H,3H)-pyrrolo[1,2-c][1,3,2]-oxazaborole in toluene is added. The mixture is cooled to an internal temperature of 0-2° C. and while maintaining an internal temperature of 0-2° C., 153 mL of a 1 molar solution of BH3 in THF is added over 1-2 hours. The reaction is stirred for another hour at an internal temperature of 0-2° C. and then quenched by addition of 65 mL methanol. The resulting solution is warmed to 25° C. and concentrated to a volume of 250 mL (50° C./200 mbar). To this concentrate is added a mixture of 713 mL water and 37 g HCl 37%. During the addition 8-(phenylmethoxy)-5-((R)-2-chloro-1-hydroxy-ethyl)-(1-H)-quinolin-2-one precipitates as a nearly colourless precipitation. The resulting suspension is stirred for 30 minutes at 25° C., filtrated and washed with 220 mL water in several portions. Drying in a vacuum drier at 50° C. for 12 hours results in 47.41 g of 8-(phenylmethoxy)-5-((R)-2-chloro-1-hydroxy-ethyl)-(1H)-quinolin-2-one as a slightly yellowish powder.
