dichloropyrazine

I would like to present you today a reaction I have performed a long time ago (in a galaxy far, far away....), and which can be very useful for different purposes.

As you probably know or should know , the regioselective chlorination of pyridine or quinoline N-oxide in the position 2 can be achieved by treatment with phopshorous oxychloride as chlorinating agent.



But, I have realized this reaction on the pyrazine-1,4-dioxide, if you apply the "classic" mechanism on this structure, you should have either the 2,5-dichloro or 2,3-dichloropyrazine, but of course it is not the case and the only compound isolated is the 2,6-dichloropyrazine.




Unfortunately, I have no explanation for this I only know that when the position 6 is blocked then the chlorination occurs in 5 and when position 6 and 5 are blocked the chlorination is in 3.
A don't have the exact references but they were J Het Chem in the mid 80's from a Yamamoto.

SYNTHESIS OF 2,3-PYRAZINEDICARBOXYLIC ACID

I will start this blog with a quite old but very interesting synthesis of pyrazine dicarboxylic acid.

This synthesis starts with the formation of quinoxaline, by the reaction of glyoxal and o-phenylendiamine in water with a 85-90% yield(1). Then the benzene fused ring is cleaved with a hot aqueous potassium permanganate solution (2), the mixture is cooled at room temperature and acidified with a 36% hydrochloric acid (3). The crude material is filtered off and recristallized in acetone to give the 2,3-pyrazinedicarboxylic acid with a 75-77% yield.

Interestingly, this synthesis can be applied to quinolines, isoquinolines and naphtalenes to provide the corresponding dicarboxylic derivatives.


For more information:

2,3-PYRAZINEDICARBOXYLIC ACID

Organic Syntheses, Coll. Vol. 4, p.824 (1963); Vol. 30, p.86 (1950).

Reuben G. Jones and Keith C. McLaughlin.