The present invention relates to a method for preparing 2-[2-(2-chlorothiazol-5-yl)-2- hydroxy-ethyl]sulfanyl-6-hydroxy-3-methyl-5-phenyl-pyrimidin-4-one or a tautomer thereof or enantiomerically enriched forms thereof, to 2-[2-(2-chlorothiazol-5-yl)-2-hydroxy-ethyl]sulfanyl-6-hydroxy-3-methyl-5-phenyl-pyrimidin-4-one or a tautomer thereof or enantiomerically enriched forms thereof, and to the use thereof as intermediate in the preparation of 2,3-dihydrothiazolo[3,2-a]pyrimidinium compounds, specifically of 3-(2-chlorothiazol-5-yl)-8-methyl-7-oxo-6-phenyl-2,3-dihydrothiazolo [3,2-a]pyrimidin-4-ium-5-olate and enantiomerically enriched forms thereof.