Pyridazino triazines

Structurally related sets of triazinoquinoline, triazinoisoquinoline and pyridotriazine derivatives have been synthesized and their binding to benzodiazepine receptors studied <06EJM445>. Pyridazino[3 ,4 3,4]pyrazolo[5,l-c]-l,2,4-triazines have been prepared and their antimicrobial activity evaluated <06PS809> <06PS2505>. 

Pyridazino[2,3-h]benzo[l,2,4]triazine 197 was prepared (84CL1197) by boiling the triazolobenzotriazole 196 with dimethyl acetylenedicarboxylate in toluene. Compound 197 behaves as a stable free radical. 

The zwitterionic pyrido[l,2- ]pyridazino[3,4-e][l,2,4]triazines 794 and 795 were prepared from furopyridotriazinium salt 793 by reaction with... 

Only a few nonazapteridines have had their UV spectra reported since CHEC-II(1996). Thus, the imidazo-fused pyridazino[6,5-( ]-l,2,4-triazines 23 show XmaiL values (dioxane) at 325 and 410nm <1999CHE376, 1999KGS426>, and the l,3-oxazino[4,5-( ]-l,2,4-triazines 25 show maximum absorption at 290nm <2003ARK98>. 

The reaction of the zwitterionic pyridazino[3,4-< ]-l,2,4-triazine 31 with methyl iodide gave the corresponding iV-methyl compound 32 via selective alkylation on the triazine N-1 (Equation 3) <2003ARK62>. 

The reaction of the pyrido-fused pyridazino[3,4-< ][l,2,4]triazinium compound 105 with secondary amines results in the ring-opening of the pyridine moiety to yield dienyl-substituted pyridazino[3,4-< ][l,2,4]triazines of which the pyrrolidine compound 106, shown in Scheme 15, is typical <2003ARK62, 1998AC0285, 1995JOC4919>. Compound 106 has been the subject of a detailed study and has been shown to react as a diene in the presence of fumaronitrile and A -phenylmaleinimide to give the Diels-Alder adducts 107 and 108, respectively <2003ARK62>,... 

The benzoylmethyl-substituted condensed triazinones 118 undergo condensation with aryl hydrazines in boiling propan-2-ol or hexan-l-ol to produce the corresponding hydrazones 119 which are easily cyclized upon boiling in neat phosphorus oxychloride to give the novel condensed pyridazino[6,5-i ]-l,2,4-triazines 120 shown in Scheme 17 <1999CHE376, 1999KGS426>. 

In common with most other sections in this chapter, progress in areas other than the azapteridines is limited to only a few publications. Thus, as shown in Equation (25), the amino-(thioxo)-triazine 161 acts as the 3-heteroatom component and undergoes a regiospecific cyclocondensation reaction with the dichlorocinnoline 160 to give the condensed pyridazino[3,4-( ]-l,3,4-thiadiazine tetracycle 162 via loss of two units of HCl <2000PS315>. 

The arylfuro-fused pyrido[l,2-/ ][l,2,4]triazinium salt 179 undergoes reaction with methyl hydrazine to give the zwitterionic pyrido-fused pyridazino[3,4- ][l,2,4]triazine 31 as shown in Scheme 32 <2003ARK62, 1997CC757>. Nucleophilic attack of the hydrazine at the bridgehead results in the elimination of an enol that then allows ring closure via attack of the other hydrazine nitrogen onto the carbonyl of the keto tautomer. 

It was reported that 7-chloro-3-phenyl-4H-pyridazino[6,1 -c ]-1,2,4-triazine underwent reaction with hydrazine to give the unexpected product (146) (69AC(R)552). However, it was later established that the assigned structure for this reaction product was incorrect, and the correct hydrazino structure (147) for this product was confirmed by an independent synthesis (70S180). 

NMR was used to establish structure (119) as the predominant tautomer of a benzo fused pyridazino[3,4-e]-1,2,4-triazine derivative. In the proton NMR spectrum of compound (119), H-6 appears as a singlet at S 13.62. This is replaced by a doublet, however, when (119) is isotopically labeled at position-5 with a l5N atom. The small coupling constant of this doublet (/= 8 Hz)... 

Some pyridazino[4,5-e]-1,2,4-triazine derivatives of the type (514) can act as photosynthetic... 

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