Diazins

Chemical shifts of pyridine and the diazines have been measured as a function of pH in aqueous solution and generally protonation at nitrogen results in deshielding of the carbon resonances by up to 10 p.p.m. (73T1145). The pH dependence follows classic titration curves whose inflexions yield pK values in good agreement with those obtained by other methods. 

The cleavage of fused pyrazines represents an important method of synthesis of substituted pyrazines, particularly pyrazinecarboxylic acids. Pyrazine-2,3-dicarboxylic acid is usually prepared by the permanganate oxidation of either quinoxalines or phenazines. The pyrazine ring resembles the pyridine ring in its stability rather than the other diazines, pyridazine and pyrimidine. Fused systems such as pteridines may easily be converted under either acidic or basic conditions into pyrazine derivatives (Scheme 75). 

Oxidation of A-aminoazetidines (19), deoxygenation of A-nitrosoazetidines (20) and direct deamination of azetidines (21) with difluoroamine leads to cyclopropanes (23) by extrusion of nitrogen from a diazine intermediate (22) (63JA97). A further interesting ring contraction occurs in the Ag" catalysed solvolysis of the A-chloroazetidine (24), which appears to involve the intermediate cation (2S) (7ITLI09). 

Chemical DesignationsDiethylenediamine Hexahydro-l,4-diazine Hexahydropyrazine Lumbrical Piperazidine razine hexahydride Chemical Formula NHCHjCHjNHCHjCHj. Observable Characteristics - Physical State (as shipped) Solid Color White Odor. Mild, aminelike. 

The CNDO method has been modified by substitution of semiempirical Coulomb integrals similar to those used in the Pariser-Parr-Pople method, and by the introduction of a new empirical parameter to differentiate resonance integrals between a orbitals and tt orbitals. The CNDO method with this change in parameterization is extended to the calculation of electronic spectra and applied to the isoelectronic compounds benzene, pyridine, pyri-dazine, pyrimidine and pyrazine. The results obtained were refined by a limited Cl calculation, and compared with the best available experimental data. It was found that the agreement was quite satisfactory for both the n TT and n tt singlet transitions. The relative energies of the tt and the lone pair orbitals in pyridine and the diazines are compared and an explanation proposed for the observed orders. Also, the nature of the lone pairs in these compounds is discussed. 

Ingham describes two by-products isolated in these reactions, (a) arylene-mandeloamides (8) formed in the presence of water and (b) diazines (11) resulting from dimerization of the chloroimine. Reconsideration by Comforth and Comforth demonstrated that reaction of 5 with water actually produces oxazolidone 9/... 

Quinazoline (1,3-diazanaphthalene) was prepared by Gabriel in 1903 although the first derivative tvas synthesized by Griess 34 years earlier. The name was proposed by Widdege. Other names such as phenmiazine, benzo-l,3-diazine, and 5,6-benzopyrimidine have occasionally been used. The numbering suggested by Paal and Busch (1) is still in use. ... 

Chlorophthalazine is quite reactive to many basic nucleophiles but reacts sluggishly with aqueous or alcoholic alkali. In contrast, it is very rapidly hydrolyzed by warm, concentrated hydrochloric acid as are its diazine isomers. In hydrolysis with very dilute acid or with water, it forms some phthalazinone but mostly the self-con-densation product which hydrolyses to give 2-(l -phthalazinyl)-phthalazin-l-one (70% yield). Such self-condensations in diazanaph-thalenes and in monocyclic azines are always acid-catalyzed (Sections II, C and III,B). With methanolic methoxide, 1-chlorophthalazine (65°, few mins), its 7-methoxy analog (20°), and 1,6- and 1,7-dichlorophthalazines (20°) readily undergo mono-substitution. 

No kinetic data or semi-quantitative comparisons among themselves or with other diazines are available. The most reactive derivative is expected to be the 4-substituted-l,6-naphthyridine (425), with 2-substituted-1,6- and l-substituted-2,7-naphthyridines (426) somewhat less reactive, all three positions being activated by two ring-nitrogens by resonance. Other positions also activated in this way... 

The oxime of bromoacetylfurazan 123 was converted into the amine 125 by treatment with hexamethylenetetramine and subsequent acidic hydrolysis. Oxa-diazine derivative 126 was made from the amine and formaldehyde in 57% yield (Scheme 73) (97ROC1760, 97ZOR1844). 

Synthesis of tritium-labeled biologically important diazines 99UK254. 

Reactions ofpotentially tautomeric methyl andmethylene derivatives of diazines with N-electrophiles 98KGS147. 

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