Fused pyrimidine derivatives R 0515 Synthesis and Molecular Design of 4,8-Diaryl-and 4,8-Di(arylethynyl)pyrido[4,3-d]pyrimidines: Potential Applications in Nonlinear Optics. Diazines Part 49. -The new push-pull compounds (VI), (IX), and (XI) with a pyrido[4,3-d]pyrimidine system as the central core are synthesized using Suzuki and Sonogashira cross-coupling reactions. Incorporation of triple and double bonds as spacer improves the nonlinear optical properties. -(BUSCH, A.; TURCK, A.; PLE*, N.; J. Heterocycl. Chem. 45 (2008) 2, 417-424; Lab. Chim. Org. Fine Heterocycl., IRCOF, Inst. Natl. Sci. Appl. Rouen, F-76131 Mont-Saint-Aignan, Fr.; Eng.) -H. Haber 30-156