Synthesis of Pyridazino [4,5-e] [1,3,4] thiadiazines and the Ring Contraction to Pyrazolo [3,4-d] pyridazines through Extrusion of Sulfur

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Cyclization of 2-substituted 5-[(α-bromobenzylidene) hydrazino)]-4-chloro-3 (2H)-pyridazinones (2) with potassium thioacetate, followed by deacetylation, provided new ring system derivatives, 7-substituted 2-phenyl-4H-pyridazino [4,5-e] [1,3,4] thiadiazin-8 (7H)-ones (4). 8-Chloro and 8-amino derivatives (10) of the pyridazinothiadiazine ring were readily derived from 4-acetyl-2-phenyl-4H-pyridazino [4,5-e] [1,3,4] thiadiazin-8 (7H)-one (3d) by chlorination and subsequent amination. Ring contraction of the 8-oxo derivatives (4) to 5-substituted 3-phenyl-1H-pyrazolo [3,4-d] pyridazin-4 (5H)-ones (6), through extrusion of sulfur under basic or thermal conditions, was observed. A similar reaction occurred in the case of the 8-chloro and 8-amino derivatives (10). Probable mechanisms for these reactions and differences of reactivity between 4 and 10 are discussed.
公益社団法人日本薬学会の論文
1984-11-25