3- imidazo pyrazine oxidation

Some very clever syntheses of pyrazines were reported. Tandem Mn02-mediated oxidation followed by in situ trapping with aromatic or aliphatic 1,2-diamines was shown to give rise to quinoxalines, dihydropyrazines, pyrazines, and piperazines without the need to isolate highly reactive 1,2-dicarbonyl intermediates <03CC2286>. A new intramolecular cyclization route to highly substituted chiral 6,7-dihydro-5//-imidazo[l,5-a]pyrazin-8-ones like 157 from Meldrum s acid was developed <030L3907>, and 5-chloropyrido[3,4-6]pyrazines were prepared from 1,2-dicarbonyl compounds and 2-chloro-3,4-diaminopyridine <03H(60)925>. A synthesis of... 

Treatment of imidazo[4,5-f>]pyrazine (225 R = H) with hydrogen peroxide in glacial acetic acid gave the 4-oxide (226 R = H) as the major product (50%) and the 4,7-dioxide (227 R = H) as the minor product. A 4-oxide was also obtained from the 1-methyl- and the l-(2,3,5-tri-0-acetyl-j8-D-ribofuranosyl)-imidazo[4,5-f)]pyrazine, in the latter case by means of MCPBA (73JMC643). Other 4-oxides and 4,7-dioxides have been prepared 75KGS690). 

This ring system has also been called l,3a,6-triazaindene and numbered as in formula 1. A third alternative numbering system (2) has also been used on one occasion. Partly reduced derivatives of imidazo[l,2-a]pyrazine have been referred to as imidazo[l,2-a]piperazines and others, as imidazolino[l,2-a]pyrazines. The majority of papers on this heterocycle are of recent origin and concern the structure and oxidation products of Cypridina luciferin, a bioluminescent substance isolated from Cypridina hilgendorfii, a small crustacean. 

PMR spectrum (in CDCI3) of imidazo[l,5-a]pyrazine and its 7-oxide are give in Figure 1. Ultraviolet and PMR details have also been reported for the 3-methyl, the 8-amino, and the 3-(2-pyrazinyl) ° compounds. More recently PMR data have been published for a variety of 3-substituted compounds. Several substituted imidazo[l,5-a]pyrazines have been studied using NMR spectroscopy. " ... 

Treatment of the unsubstituted compound 103 with hydrogen peroxide in glacial acetic acid resulted in the isolation of two iV-oxides. The minor product (8%) was the 4,7-dioxide 105, and the major product (50%) was suggested to be the 4-oxide 104. This assignment was supported by the similarity of the compound s UV spectrum to that of the l-methyl-4-oxide 81, which had been obtained from the pyrazine 87 by an unambiguous route. A 4-oxide was also obtained when the acetylated nucleoside analogue 106 was oxidized with mefa-chloroperbenzoic acid. There has been a recent Russian communication on the chemistry of imidazo[4,5-ft]pyrazine N-oxides. ... 

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