Reaction of N-acetyliminopyridazinium ylide (3) with benzyne afforded 1, 3-dipolarcycloadduct (4). Photolysis of the cycloadduct (4), having alkoxy group in the 3-position of the pyridazine ring, afforded α-alkoxynaphthalene (5), and 3-(2-acetoamidophenyl) pyridazine (7). Photolysis of 4a did not give naphthalene, but afforded indazolo [2, 3-b] pyridazine (6). Reaction of 4 with base afforded 3-vinylindazole (8). indazolo [2, 3-b]4, 5-dihydropyridazine (9). Reaction of 2H-pyridazinone 1-oxide (22) with benzyne afforded the 1, 3-cycloadduct (23), followed by fission of N-O bond to give pyridazinone substituted with 2-hydroxyphenyl group (24). The reaction mechanisms are also discussed.