A general route to 1,2,4-trisubstituted pyrimidines is described in one to three steps from a common key precursor, diazadienium iodide 2. An efficient preliminary [4+2] cyclocondensation reaction between the azabutadiene building block 2 and various iso(thio)cyanates constitutes an original construction of the pyrimidine skeleton. Subsequent structural modifications on the heterocycle allow the elaboration