Pyridazino thiazine-diones

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. 

A one-pot tandem method for the synthesis of pyridazino[4,5-fc][l,4]thiazine-diones via Smiles rearrangement has been reported (Scheme 173). ... 

---