5.6- Dihydro-5,6-dioxo pyrazine

Heating either trimethyl 2-methyl-6-ethylidene-2,6-dihydro-l//-pyrido[l,2a]-pyrazine-7,8,9-tricarboxylate or tetramethyl 1,2-dimethyl-2,9a-dihydro-l//-pyrido-[l,2-a]pyrazine-6,7,8,9-tetracarboxylate in dilute HC1 gave dimethyl 2-methyl-7-propionyl-l,6-dioxo-2,6-dihydro-l//-pyrido[l,2-a]pyrazine-8,9-dicarboxylates (62JCS1510). 1,12-Dihydroxyper-hydrodibenzo[ac]pyrazine was prepared from l-(2-tetrahydrofuryl)-9-hydroxyperhydropyrido[l,2-a]pyrazine in AC2O saturated with HBr at 95-100°C (61BSF2135). 

Fission and desulfurization of 2,2-dimethyl-5,8-dioxo-2,3,6,7,8,8a-hexahydro-5//-(hiazolo[3,2-a]pyrazine-3-carboxylic acid (140), by treatment with Raney nickel in aqueous ethanolic sodium bicarbonate at 20°C during 12 h, gave 1-(I -carboxy-2-methylpropyl)-3,6-dihydro-2,5( 1 //,4//)-pyrazinedionc (141) in 58%... 

Again, only one example of this synthesis has been reported. Like the analogous substrate (140), isobutyl 1,1 -dimethyl-5,8-dioxo-1,5,6,7,8,8a-hexahydro-3//-thia-/oIo13,4-a pyrazine-3-carboxyIic acid (142) underwent hssion and desulfurization (on stirring with ethanolic Raney nickel at 20°C for 12 h) to afford an hydropy-razine, this time l-isobutoxycarbonylmethyl-6-isopropyl-3,6-dihydro-2,5(l//, 4H)-pyrazinedione (143) in 89% yield.1255... 

Furan 2-Aminomethyl-5-(2,4-dioxo-1,2,3,4-tetrahydro-pyrimidino)-2,5-dihydro- IV/lc, 578 Imidazo(l,2-a]pyridin 1,5-Dimethyl-8-nitro-7-oxo-l,2,3,7-tetrahydro-E15/3, 2790 [cycl. (R2N)2C = CH-N02 4- Diketen] 1,3-Oxazol 4-Cyan-5-(diethoxy-methylen-amino)- E4, 565 (Het — NH2 + Orthoester) Pyrazin 3-Amino-2-methoxycarbo-nyl-5-propanoyl- E9b/2, 324 (H - CO-R)... 

Attempted oxidation of the 3-oxo compound 96 with potassium permanganate resulted only in ring breakdown. Nevertheless a solution of this reagent in acetone is commonly used to oxidize compounds such as the dihydro derivative 97 to the aromatic system without further oxidation occurring. Oxidation of the tetrahydro oxo compound 98 with potassium permanganate in 2M sodium hydroxide solution at room temperature gives the 2-oxo compound 99. This compound is sensitive to oxidation, and the use of iodine has been recommended for this conversion. If alkaline potassium ferricyanide is used, the product formed is the dioxo derivative 100. The dioxo compound is also obtained from l,2-dihydro-2-oxo- or 3,4-dihydro-3-oxopyrido[2,3-b]pyrazine under the same conditions. Recently ferric chloride has been used to aromatize a series of dihydropyrido[2,3-b]pyrazines. ... 

Dioxo-2.7-diphenyl-4.9.dihydro.dipyra azolo[l.S-a, l. S -d]pyrazin 26 II288. 

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