1.2.4- Triazine A-oxides

Synthesis, properties, and applications of nonsymmetric triazinones 99MI26. Transformations of 1,2,4-triazines by the action of C-nucleophiles 98ZOR327. 1,2,4-Triazine A -oxides and their annelated derivatives 98UK707. 

In the mass speetra of 1,2,4-triazine A-oxides, moleeular ion peaks and [M -16]" or [M — 17]" peaks were observed. The fragmentation pattern for the 1,2,4-triazine A-oxides does not allow determination of the position of the A-oxide group (71JHC317, 71LA12, 78JOC2514, 98ZOR423, 98ZOR429). 

All of the general classes of cr -adduct aromatization were found to occur in the reactions of 1,2,4-triazine A-oxides with various nucleophiles. From this point of view, the 1,2,4-triazine A-oxides are a very convenient substrate for the Sj reaction studies. 

The highly 7r-deficient character of the 1,2,4-triazine ring increases the nucle-ophilicity of the methyl group in methyl-1,2,4-triazine A-oxides in reactions with electrophilic alkenes and aldehydes. Thus treatment of the 6-methyl-3-phenyl-1,2,4-triazine 4-oxide 113 with l-(dimethylamino)-l-ethoxyethylene leads to the... 

Azine approach. The fused uracil (58) has been prepared from 5-amino-l,3,6-trimethyl-uracil diazotization of the latter yields a fused triazine A-oxide (57), which has its triazine ring transformed into an isoxazole ring by tin(II) chloride treatment (62USP3056781). 

The three isomeric 1,2,4-triazine A-oxides can be employed as substrates in reactions with nucleophilic reagents. However, they are specific with respect to the fact that two opposing factors affect charge distribution in their molecules. The electron-withdrawing ability of the N-oxide function seems to activate the ring carbon atoms for a nucleophilic attack... 

Shaw has described the oxidation of triazines with peracetic acid (very poor to high yields) and the preparation of 2,6-diamino-4-methyl-l,3,5-triazine A-oxides from potassium dicyanoacetamide and hydroxylamine (24-69% yield) <62JOC3890>. Kaugars and Watt reported the formation of triazine A-oxides from two equivalents of an amidoxime with ethyl orthoacetate, but only in low to moderate yields (13-48%) (see Section 6.12.9.2.2). 

In the mass spectra of 1,2,4-triazine A -oxides, molecular ion peaks M and the peaks [M-16], corresponding to elimination of an oxygen atom, have been observed. Unfortunately, the fragmentation pattern for 1,2,4-triazine A -oxides does not allow the position of the A -oxide group to be established <1998RJ0393, 1998RJ0393>. 

In a similar way, cyanation of two triazine A -oxide fragments in 2,6-disubstituted pyridine 83 affords the corresponding dicyano derivatives 84 in 70-85% yields (Scheme 47) <2002TL4923, 2003JOC2884, 2003S2400>. 

New, general synthetic approaches to triazine A-oxides have not been described. 

A new method for the synthesis of triazine-A oxides (10) involves reacting amidoximes... 

Scheme 23 Amination of triazine A-oxides in liquid NH3/KMn04 system...

Triazine A-oxides can be obtained by two genial methods by direct oxidation of the parent 1,2,4-triazmes with organic peracids, and by the formation of the A-oxide group of the 1,2,4-triazine ring by cyclization involving nitro, nitroso (isonitroso), or hydroxylamino groups. 

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