A scalable synthetic strategy to produce a large variety of unsymmetrical trisubstituted 1,3,5-triazines was developed. This protocol applied in situ formed acyl isocyanate from amide to react with amidine, introducing two substituents to the 1,3,5-triazinone ring with a low production cost and a simple workup procedure. The scalability of this method was demonstrated by translating a small-scale procedure to a multi-kilogram-scale synthesis. Chlorination and a further coupling reaction with various nucleophiles could provide unsymmetrical trisubstituted 1,3,5-triazines bearing diverse functional groups.