This invention relates to the synthesis of chemical compounds and particularly to methods for the preparation of (4,6-dihalo-pyrimidin-5-yl)-acetaldehydes. The methods involve preparing a compound of the following general formula V from a compound of the following general formula IV through hydrolysis under the action of mercury dichloride and calcium carbonate, according to the following equation: wherein X is Cl or Br. The methods offer the benefits of use of highly available materials, high step yields, moderate reaction conditions, simply post-processing and purification, and suitability to industrialized production.