Pyridazine derivatives. Part 21: Synthesis and structural study of novel 4-aryl-2,5-dioxo-8-phenylpyrido[2,3-d]pyridazines

New substituted 4-aryl-2,5-dioxo-8-phenylpyrido[2,3-d]pyridazines 4a-f have been prepared in one step from the corresponding arylidene substituted Mel drum's acid (1) and 5-amino-6-phenyl-3(2H)-pyridazinone (2) in good yields. Semiempirical theoretical calculations (AM1) reveal two favoured conformat ions (A and B) for compounds 4a-f, with a screw boat conformation in the py ridone system and a planar pyridazinone ring. X-Ray crystallographic analys is shows that in the solid state, conformation A bearing the phenyl ring in a pseudoaxial position is the most stable. Compounds 4a-f fulfil, from the structural point of view, all the requirements needed for exhibiting cardi otonic effects. (C) 2000 Elsevier Science Ltd. All rights reserved.