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Communication | Regular issue | Vol 22, No. 3, 1984, pp.479-484
Published online, 1st January, 1970
DOI: 10.3987/R-1984-03-0479
Synthesis of Pyrazolo[3,4-d]pyridazine Derivatives — Two Comparable Approaches, Ring Contraction through Extrusion of Sulphur and Photochemical Cyclisation

Kenji Kaji, Hiromu Nagashima, Yusho Ohta, Shigeto Nagao, Yoshihiko Hirose, and Hirohisa Oda*

*Gifu Pharmaceutical University, 6-1 Mitahora-higashi 5-chome, Gifu 502-8585, Japan


Ring contraction of 7-substituted 2-phenyl-4H-pyridazino[4,5-e][1,3,4]thiadiazin-8(7H)-ones (5a-d) to 5-substituted 3-phenyl-1H-pyrazolo[3,4-d]pyridazin-4(5H)-ones (7a-d), through base-induced extrusion of sulphur, is described. Similar reactions proceed, not only on the 4-acetyl derivatives (4a-d) in basic media, but on 5a and the 4-methyl derivative (6a) thermally. Probable mechanisms of these reactions are discussed. A comparable approach to the ring contraction, photochemical cyclisation of 2-substituted 5-(1-alkyl-2-benzylidenehydrazino)-4-chloro-3(2H)-pyridazinones (9a-e) to the corresponding 1-alkylpyrazolo[3,4-d]-pyridazinone derivatives (8a-e) is also performed.