Fission, Rearrangement, or Cyclocondensation of Nuclear Halogenopyrazines

Halogenopyrazines undergo the occasional ring fission or rearrangement as well as a variety of useful cyclocondensations to afford annelated derivatives. Such reactions are typified in the following examples  

5-Tetrafluoro-3,6-bis(heptafluoroisopropyl)-2,5-dihydropyrazine (197) gave a separable mixture of perfluoro-[3-methyl-2-(methyleneamino)but-l-ene] (198) and the gas, perfluoroisobutylronitrile (199) [hv (254 nm), 2 weeks 38 and 35%, respectively].17 

3- Dichloropyrazine (204, R = H) gave l,3-dithiolo[4,5- ]pyrazine-2-thione (203) [(KS)2C=S (made in situ), Me2NCHO, 45°C, 3 days 60%] analogues likewise.264 

3-chloropyrazine (57%) then neat intermediate, 220°C, 2 h 47%] 600 also some aza and oxa analogues likewise but without isolation of intermediates.777-1268 

5-Amino-6-chloro-2,3-pyrazinedicarbonitrile (210, R = H) also gave the foregoing product (208) [pyridine, 20°C, 24 h 73% perhaps via aerial oxidation of the intermediate (211)]1393 or 5,10-dihydrodipyrazino[2,3-fc 2, 3 - ]pyrazine (209, R = H) (Et3N, Me2NCHO, reflux, 10 h 78%) 1598 several 5,10-dialkyl analogues (209, R = alkyl) were made similarly.1598 

3-Dichloropyrazine (204, R = H) gave 8-chloro-107/-pyrazino[2,3-fc] [1, 4]benzothiazine (205) [2-amino-4-chloro(thiophenol). EtsN, Me2NCHO, 20°C, 5 h, then 150 C, 6 h intennediate 2-(2-amino-4-chlorophenylthio)- 

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