Several pyrimido [4, 5-b] quinolines, flavin analogues, have been prepared by assisted microwave intramolecular cyclization of N4-substituted-2, 4-diamino-6-chloropyrimidine-5- carbaldehydes. The reaction takes place with hydrolysis of amino-group and chlorine. Particularly valuable features of this method included the broader substrate scope and operational simplicity as well as increased safety for small-scale high-speed synthesis.