Pyridazines structure

Oxidation of 2-substituted l,l-dimethyl-2-ethylhydrazines with mercuric oxide gives products assigned the pyridazine structures 115, accompanied by pyrazines. From cts-dibenzoylstilbene oxide and p-tosylhydrazine, five products were obtained, among them tetraphenylpyridazine in 6% yield. 

Pyridazines and triazines are not usually biosynthesized in plants. The exception is azathymine (6-methyl-l,2,4-triaz-ine-3,5(2H,4H)-dione) which has been identified in modified bases from DNA of tobacco mosaic virus (3973). The majority of the identified pyridazines and triazines in tobacco are believed to originate from residues of agronomic chemicals. The pyridazine structure is found in herbicides containing... 

Teoh, M. M., Liu, S. L., Chung, T. S. (2005). Effect of Pyridazine Structure on Thin-Fihn Polymerization and Phase Behavior of Thermotropic Liquid Crystalline Copolyesters. J. Polym. Sci. B, 43(16), 2230-2242. 

Table V shows some of the work we did with variation in the basic pyridazine structure, and also with related nitrogen heterocycles. Moving...

Galiullina SV, Zakharova VM, Kantin GP, Nikolaev VA (2007) Chemistry of diazocarbonyl compounds XXX. Development of a synthetic approach to pyridazine structure via Wittig reaction of fluoroalkyl-containing diazo keto esters. Russ 1 Org Chem 43 607-614... 

Pyridazine-3(2//)-thiones exist in the thione form (14), as is evident from an X-ray structure analysis of pyridazine-3(2//)-thione. 6-Mercaptopyridazine-3(2//)-thione is predominantly in the monothiolmonothione form (15) in aqueous solution and in the solid state, 6-hydroxypyridazine-3(2//)-thiones are in the hydroxythione form (16) and 6-aminopyridazine-3(2//)-thiones exist in the aminothione form (17) for further details see (73HC(28)755). Cinnoline-4(l//)-thiones and phthalazine-l(2//)-thione have been shown on the basis of UV data and ionization constants to exist in the thione forms. 

N-protonation the absolute magnitude of the Ad values is larger than for Af-methylation <770MR(9)53>. Nuclear relaxation rates of and have been measured as a function of temperature for neat liquid pyridazine, and nuclear Overhauser enhancement has been used to separate the dipolar and spin rotational contributions to relaxation. Dipolar relaxation rates have been combined with quadrupole relaxation rates to determine rotational correlation times for motion about each principal molecular axis (78MI21200). NMR analysis has been used to determine the structure of phenyllithium-pyridazine adducts and of the corresponding dihydropyridazines obtained by hydrolysis of the adducts <78RTC116>. 

The tendency for fragmentation by loss of N2, when compared with pyridazine, is reduced in the case of phthalazine where losses of HCN become important (Scheme 3). This is supported by quantum mechanical calculations which show that the structure (3a) better represents the ground state of the molecule than structure (3b). 

Structural problems in the pyrido[3,4-c]pyridazine series (76CPB1870) and in the fused pyridazino[4,5-6]quinoline series (80CPB3457) have also invoked mass spectral determinations. 

Pyrazino[2,3-d]pyridazin-8-one, 5-chloro-synthesis, 3, 347 Pyrazino[l, 2-a]pyrimidine reactions, 3, 350 structure, 3, 339-340 synthesis, 3, 256, 365 Pyrazino[ 1,2-a]pyrimidine, 2-hydroxy-alkylation, 3, 351... 

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... 

H,3H- Pyrrolo[l, 2-c]oxazole-l, 3-dione, 5,6,7,8-tetrahydro-IR spectra, 6, 978 [2.2](2,5)Pyrrolophane, N-aryl-rearrangements, 4, 209 Pyrrolophanes natural products, 7, 764 synthesis, 7, 771 Pyrrolophanes, N-aryl-synthesis, 7, 774 (2,4)Pyrrolophanes synthesis, 7, 771 Pyrrolo[3,4-c]pyran-4-ones synthesis, 4, 288 Pyrrolopyrans synthesis, 4, 525, 526 Pyrrolopyrazines synthesis, 4, 526 Pyrrolo[l, 2-a]pyrazines synthesis, 4, 516 Pyrrolo[2,3-6]pyrazines Mannich reaction, 4, 504 Vilsmeier reaction, 4, 505 Pyrrolo[3,4-c]pyrazole, 1,3a,6,6a-tetrahydro-structure, 6, 976 synthesis, 6, 1019 Pyrrolopyrazoles synthesis, 5, 164 Pyrrolo[l,2-6]pyrazoles synthesis, 6, 1002, 1006 Pyrrolo[3,4-c]pyrazoles reactions, 6, 1034 synthesis, 6, 989, 1043 Pyrrolo[3,4-c]pyrazolones synthesis, 6, 989 Pyrfolopyridazines synthesis, 4, 517 Pyrrolo[l, 2-6]pyridazines synthesis, 4, 297 6/7-Pyrrolo[2,3-d]pyridazines synthesis, 4, 291 2/f-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291 6/7-Pyrrolo[3,4-d]pyridazines synthesis, 4, 291... 

Amino-pyrazines and -pyridazines have been shown to exist predominantly in the amino form by infrared spectroscopic studies (cf. Table VI). Ultraviolet spectral data have been interpreted to indicate that 4-aminocinnoline exists predominantly in the imino form 256, but this conclusion, which was based on comparison of its spectrum with those of cinnolin-4-one and 4-ethoxycinnoline, is probably incorrect. Ultraviolet spectroscopic data strongly support the predominance of amino structures for 2-aminopyrazine (257) and 2-aminoquin-oxaline how ever, the former compound was at first erroneously concluded to exist in the imino form from ultraviolet spectral evidence. Isolation of two isomers of 2-amino-8-dimethylamino-3-methylphenazine, assigned the amino and imino structures 258 and 259, respectively, has been claimed, but it is very unlikely that these assignments are correct. 

A variety of 3,6-disubstituted pyridazines have been quatemized and the structures of the salts determined by unambiguous synthesis, degradation, or reactivity, On the basis of these data the following... 

Factor b above is discussed in Sections II, B, 1 II, B, 4 and II, C. A hydrogen-bonded structure such as 221 can account for the facile reaction of 5-bromouracil or for the unique, so-called hydrolyzability of carboxymethylthio-azines (237). The latter may also react via the intramolecular mechanism indicated in 136. The hydrogen-bonded transition state 238 seems a reasonable explanation of the fact that 3,4,6- and 3,4,5-trichloropyridazines react with glacial acetic acid selectively to give 3-pyridazinones while other nucleophiles (alkoxides, hydrazine, ammonia, or sulfanilamide anion) react at the 4- and 5-positions. In this connection, 4-amino-3,5-dichloro-pyridazine in liquid hydrazine gives (95°, 3hr, 60%yield)the isomer-... 

In this work the possibility of the existence of 1,2-dihydro isomer with the core structure 42 was not considered. Recently, however, it was shown that 1,2-dihydropyridazines could be prepared by careful electroreduction of the corresponding pyridazines, and that their stability depends significantly on the ring substitutions. Thus, dimethyl l,2-dihydropyridazine-3,6-dicarboxylate 43a (R = H) is reasonably stable and rearranges into the 1,4-dihydro tautomer 43b only at a more negative potential, while the tautomerization in its tetrasubstituted analog 43a (R = COOMe) occurs more readily (Scheme 14) [00TL647]. 

Chemical Name 6-Benzoyl-3-hydrazino-5,6,7,8-tetrahydropyridol[4,3<] pyridazine Common Name -Structural Formula ... 

The reaction of several substituted imidazo[4,5-c/]-, pyrazolo[3,4-r/]- and triazolo[4,5-zf]pyrid-azines 3 with ynamines, in competition with [4 + 2] cycloaddition, leads to [2 + 2] derivatives 4, which rearrange to l,2-diazocines5.7 8 The reaction seems to be sensitive to the substituents, as replacement of the electron-withdrawing group R on the pyridazine ring of the pyrazolo compound (A = N, B = CH) by chlorine completely inhibits both the [4 + 2] and [2 + 2] cycloaddition reactions. The X-ray structure of the imidazo derivative 5 (R = Ms, A = CH, B = N) reveals a tub conformation of the eight-membered ring. 

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