Benzil with 2,3-diaminopyridine

Pyrido[l,2-3][l,2,4]triazinium salts 132 could be obtained from 131 with benzil either in the presence of TEA <2001CPH(266)77> or sulfuric acid <2003ARK155> (for example, diaminopyridines 131 are generally available from 2-aminopyridines 120 via N-amination with tosyl hydroxylamine (Scheme 14) <2003ARK155>). 

When the diamino salt 9 was treated with the 2,3-furandione 10, it gave the pyrido[l,2,-6][l,2,4]triazinone 11, whose reaction with base gave the respective monobenzoyl derivative (89CB1935). Cyclocondensation of 1,6-diaminopyridines 12 with diacetyl gave [73KGS1266 90JCR(S)186] pyridolf 1,2 b] 1,2,4]triazines 13. On the other hand, reaction with benzil was unsuccessful. 

Pyrido[l,2-7][l,2,4]triazinium salts 113 can be obtained from 112 with benzil in the presence of either base <2001CPH77> or sulfuric acid (Scheme 73) <2003ARK(xiv)155>. In an analogous reaction, 1,2-diaminopyridines 114 are transformed into 2,3,6-trioxopyridotriazines 115 by treatment with oxalyl chloride in the presence of triethylamine (Scheme 74) <1998SC3331, CHEC-III(12.03.2A4)237>. 

Diaminopyridine has been condensed with glyoxal, benzil, - diacetyl,and the pyridils 4. ° Ethyl oxalate yields the 2,3-dioxo compound. The conditions employed for these condensations can be critical. Thus glyoxal in neutral solution yields an unidentified, insoluble, infusible solid, whereas in the presence of acetic acid the reaction readily provides the parent heterocycle.The preferred method makes use of glyoxal sodium bisulfite. Many symmetrical dicarbonyl compounds have been condensed with a variety of 2,3-diaminopyridines substituted in the pyridine ring by bromo, ° chloro, methyl, " or combinations of these substituents. ... 

The condensation of 3,4-diaminopyridine with glyoxal hydrate in alcohol gives a 50% yield of the parent heterocycle m.p. 97°. This method is more convenient than the use of the bisulfite compound in aqueous acetic acid, which provides only a low yield of the required compound. Benzil and diacetyl and l,4-dibromobutane-2,3-dione provide the expected 2,3-disubstituted products 4 in good yields. Dimethyl oxalate reacts with 3,4-diaminopyridine in refluxing M hydrochloric acid to give the open-chain compound 5." This may be cyclized to the dioxo compound 6 by heating at 230°. 

Benzil also condenses with 23-dianuno-4,64utidine to yield 6,8-dimethyl-2,3-diphenylpyrido[2,3-b]pyrazine (K-203). The reaction of diacetyl with 3,4-diaminopyridine yields 23-din ethylpyrido-[3,4-b] pyrazine (IX-204). ... 

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