[Display omitted] • Novel Pd(II)-catalyzed C5 site-selective Suzuki monocoupling of 3,5-dichloropyridazine developed. • Inexpensive and commercially available raw materials employed. • A shorter four-step route optimized giving an overall yield of over 73 %. An efficient and concise method is hereby reported for the synthesis of pyrido[3,4- c ]pyridazin-8(7H)-ones from the commercially available material, methyl 4,6-dichloropyridazine-3-carboxylate. The four-step reaction process involves Suzuki coupling, Buchwald coupling, ammoniation, and intramolecular cyclization. The advantage of this route represents the development of a novel C5 site-selective Suzuki monocoupling of 3,5-dichloropyridazine, with an overall yield of over 73 %. [ABSTRACT FROM AUTHOR]