Tetrahydropyridazine-3,6-dione

Substituted-tetrahydropyridazine-3,6-dione-3-hydrazones 27 react with strong carboxylic acids and with some acyl chlorides to give A-acyiated products and/or triazolo[4,3-6]pyridazines. Derivatives of this type are also obtained in reactions of 27 with triethyl orthoformate and orthoacetate. In reactions with phosgene, triazolo[4,3-6]pyrazine-3,6-diones are obtained and with oxaly chloride pyridazino[6,1-c]triazine-3,4,7-triones are formed (Scheme 4) <96MI01 97CA( 126)251121>. 

The steric course of electrophilic additions of BrN3, IN3, and iV-bromosuccinimide (NBS) to the tetrahydropyridazine ring of benzo[g]pyridazino[l,2- ]phthalazine-6,13-dione system, for example, 130, has been studied and the results are shown in Scheme 12 <1997CJC348>. 

Figure 12 1,2,3,6-Tetrahydropyridazine containing 1,4-dihydrobenzo p]pyridazino[1,2-b]phthaiazine-6,13-diones.

Disiloxy-l,2,3,6-tetrahydropyridazines. A soln. of 4-phenyl-3//-l,2,4-triazole-3,5(4//)-dione in chloroform treated with 2,3-bis(/cr butyldimethylsilyloxy)-1,3-butadiene in the same solvent, and stirred for 1 h at room temp. 6,l-bis(tert-butyldimethylsilyloxy)-5,8-dihydro -1//-[1,2,4] triazolo[1,2-a]pyridazine-1,3(2//)-dione. Y 90%. F.e., also 4,5-disiloxy-3,6-dihydro-2./r-l,2-oxazines from nitroso compds., and 4,5-disiloxy-3,6-dihydro-2//-l,2-thiazine 1-oxides from N-thionylsul-fonamides, s. W. Ried, U. Reiher, Chem. Ber. 121, 185-6 (1988). 

---