1.3- Thiazine-4,6-diones synthesis

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). ... 

Diones are normally synthesized from /3-hydroxy acids in two steps first, conversion into carbamates by reaction with sodium cyanate, and then cyclization with thionyl chloride (Scheme 103) (54JCS839). Alternative preparations utilize oxetanes, which may be combined either with isocyanates in the presence of boron trifluoride (68JAP6808278) or with S-alkylthioureas (Scheme 104) (69ZOR1844). In the last example the initial products are imines (224) which may readily be hydrolyzed to the required diones. Similar methods can be applied to the synthesis of tetrahydro-l,3-thiazine-2,4-diones, and, for instance, the 4-oxo-2-thioxo derivative (225) is obtained from /3-propiolactone and dithiocarbamic acid (Scheme 105) (48JA1001). 

Thiazine-3,4-dione, tetrahydro-synthesis, 3, 1030 Thiazines, 3, 995-1038 S,S-dioxides pyrroles from, 4, 153 nomenclature, 3, 995 pyrroles from, 4,152... 

The majority of syntheses of 1,4-thiazines involve the elimination of HL from species of type 11. Precursors of type 11a are not usually isolable compounds but are generated as intermediates. Two methods for the formation of such intermediates have been described one utilizes tetrahydro-1,4-thiazine-3,5-diones as starting materials, and the other requires diacyl sulfides and ammonia. Thus the synthesis of 2/f-l,4-thiazine (6), reported in 1948, was achieved by heating compound 16 at 450°C in the presence of powdered aluminum. Potentially, the procedure may be applied to the preparation of thiazines variously substituted at positions 2 and 6 however, the low yield (13%) achieved for the parent compound is a detraction. It was initially claimed that the reaction of diphenacyl sulfide with ammonia gave 3,5-diphenyl-4H-l,4-thiazine subsequent studies, however, revealed that the product was the 2//-tautomer 3,5-Diaryl-2/f-l,4-thiazines and... 

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