Abstract: The invention relates to a process for the preparation of substituted pyrimidines of formula I, wherein R1, R2, R3, R4 and X are as defined in claim 1, which comprises reacting an amidine of formula II, or a salt thereof, with a 3,3-disubstituted vinylcarbonyl compound of formula III wherein L represent a halogen atom or a group of formula —X—R2, (a) in an inert solvent, in the presence of a base and a compound of formula IV H—X—R2  (IV) in the event that L represent a halogen atom, or (b) in an inert solvent and in the presence of a base, in the event that L represents a group of formula —X—R2.