A study of formylation of 6-aminopyrimidines leads to the conclusion that the formylation at C5 occurs only when there is no contribution of heteroaromaticity in the pyrimidine ring and that the corresponding pyrimidoformamides are formed in heteroaromatic pyrimidines.Once 4aminopyrimidin-4(3H)-one-5-carboxaldehydes were prepared, a series of 7-arylpyrido[2,3d]pyrimidines derivatives were synthesized by a Friedländer type reaction with acetophenones under solvent-free conditions and in the presence of BF 3 -Et 2 O.The yields of 7-arylpyrido [2,3d]pyrimidines range from moderate to good and the reaction times were quite short.