Method for preparing 2-[2-(2-chlorothiazol-5-yl)-2-oxo-ethyl]sulfanyl-6-hydroxy-3-methyl-5-phenyl-pyrimidin-4-one

A method for preparing 2-[2-(2-chlorothiazol-5-yl)-2-oxo-ethyl]sulfanyl-6-hydroxy-3-methyl-5-phenyl-pyrimidin-4-one of formula (I):

• or a tautomer thereof,
• which method comprises
• (a) reacting N-methylthiourea of formula 1 with a 2-phenylmalonate of formula 2 in the presence of a base
• where R1 and R2, independently of each other, are C1-C4-alkyl;
• to obtain a reaction mixture containing a pyrimidinone compound of formula 3
• wherein M+ is a cation equivalent;
• and/or a tautomer thereof;
• (b) optionally isolating the pyrimidinone compound of formula 3 or a tautomer thereof from the reaction mixture obtained in step (a) either in a form of its salt or in a thiol form;
• and
• (c) reacting either the reaction mixture obtained in step (a) without isolation of the pyrimidinone compound of formula 3 or its tautomer or the compound obtained in step (b) with 1-(2-chlorothiazol-5-yl) ethanone of formula 4
• where X is a leaving group,
• to obtain the compound of formula (I) or a tautomer thereof.