2,5 -Diethoxy-3,6-dihydropyrazine oxidation

Sammes and co-workers (314) have also shown that some piperazine-2,5-diones (89) react with an excess of triethyloxonium iluoroborate to give a mixture of cis-and rra/is-2,5-diethoxy-3,6-dihydropyrazines (90) which can be oxidized with dichlorodicyanobenzoquinone (DDQ) to 2,5-diethoxypyrazines (91) in high yield. Many similar oxidations of dihydropyrazines have recently been described (314a). 

Diniethylpiperazine-2,5-dione (34) on treatment with triethyloxonium fluoroborate in dichloromethane gave 5-ethoxy-l,3-dimethyl-2-oxo-l, 2,3.6-tetrahydropyrazine which was oxidized by DDQ in dry benzene to 5-ethoxy-l 3 dimethyl-2-oxo-l,2-dihydropyrazine (35) (1067). l,3,6-Trimethylpiperazine-2,5-dione similarly treated gave three products, one of which was assigned the structure 5-methoxy-l 3,6-trimethyl-2-oxo-l, 2-dihydropyrazine 3-benzyl-5-methoxy-l, 6-dimethyl-2-0X0-1,2-dihydropyrazine was also prepared similarly (1078). When 3,6-diethoxy-2,5"dimethyl-2,5-dihydropyrazine was refluxed with lead tetraacetate in dry benzene it gave a mixture of 2,5-diacetoxy-3,6-diethoxy-2,5-dimethyl-2,5-dihydropyrazine (36) (4 parts) and 2,5-diethoxy-3,6-dimethylpyrazine (1 part) (1068). 

Oxidation of 2,5-diethoxy-3,6-dihydropyrazine with dichlorodicyanobenzo-quinone (DDQ) formed 2,5-diethoxypyrazine (314), and the 3,6-dimethyl analogue reacted similarly (314). 2,5-Diisopropyl-3,6-dimethyl-2,5-dihydropyrazine was oxidized in alkaUne solution to 2,5-diisopropyl-3,6-dimethylpyrazine (225). Oxidation of 2,5-diethoxy-3,6-dimethyl-3,6-dihydropyrazine with lead tetraacetate in refluxing benzene gave both 2,5-diethoxy-3,6-dimethylpyrazine (minor product) and 2,5-diacetoxy-3,6-diethoxy-2,5-dimethyl-2,5-dihydropyrazine (1068). 

Piperazine Derivatives. Treatment of piperazine-2,5-diones with an excess of triethyloxonium fluoroborate gives 2,5-diethoxy-3,6-dihydropyrazines (390), which can be oxidized to the parent pyrazines (391) by dichloro-cyanobenzoquinone. c/s-Diben lpiperazin ione gives a mixture of cis- and /ra j-dihydropyrazines (390). Pyrolysis of the /ro s-isomer gives 3-benzyl-2,5-diethoxypyrazine (392) in high yield with the elimination of... 

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