Pyridazino pyridazine, 5,8-dichloro

H,6H-Pyridazino[4,5-d]pyridazine-l,5-dione, 4,8-dichloro-2,6-dimethyl-X-ray crystal structure, 3, 333 Pyridazino[l, 2-a]pyridazine-1,4-diones IR spectra, 3, 332... 

The synthesis of pyridazino[4,5-fo] [1,4]oxazine derivatives 93 (Scheme 33) from either 4-chloro-5-hydroxy- or 4,5-dichloro-2H-pyridazin-3-one derivatives 89 and 91, respectively, was examined [56]. The hydroxy derivative 89 was condensed with chloroacetamide derivative using cesiiun carbonate in acetonitrile whereas for the complementary experiments, potassium carbonate in DMF was used. In both routes the rearrangement was effective, hi route B markedly shorter reaction times were needed and higher yields were obtained. Some examples are shown in Table 5. 

The Ma group devised a facile, an inexpensive, and a metal-free synthesis of pyridazino[4,5-l>][l,4]thiazine-diones 27 via a Smiles rearrangement, obtaining the desired products in high yields (Scheme 11) (13TL3253). Optimal reaction conditions were determined to be treatment of 4,5-dichloro-2-(tetrahydro-2f/-pyran-2-yl)pyridazin-3(2fJ)-one 28 with an N-substituted mercaptoacetamide 29 at room temperature in the presence of cesium carbonate as the base and N,ALdimethylformamide (DMF) as the solvent. The authors foresee future applications of this method to the preparation of biologically active compounds. 

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