Nuclear Halogenopyrazines from Pyrazinones

Although such transformations have usually been done with neat phosphoryl chloride (or bromide), it appears that related reagents or a combination of reagents have proven more effective in individual cases. Recently used procedures are typified in the following classified examples  

Ethyl 5-oxo-4,5-dihydro-2-pyrazinecarboxylate (1) gave ethyl 5-chloro-2-pyrazinecarboxylate (2) (POCl3, reflux, 90 min 88%).1681 

2(l//)-Pyrazinone gave 2-chloropyrazine (POCl3, reflux, 50 min 84%).64 5-(I uran-2-yl )-2( I //)-pyrazinone gave 2-chloro-5-(furan-2-yl)pyrazine (3) (POCl3, 

3-Mcthyl-5-phenyl-2(l//)-pyrazinone (4) gave 2-chloro-3-methyl-5-phenylpyra-zine (5) (P0C13,175°C, sealed, 18 h 92% beware of pressure within the tube even when cooled ) 57 such a sealed reaction also converted 5-chloro-3-phcnyl-2( l//)-pyrazinone into 2,5-dichloro-3-phenylpyrazine (6) (185°C, 5 h 92%).1382 

3-Amino-5,6-dimethyl-2(l//)-pyrazinonc (7) gave 3-bromo-5,6-dimethyl-2-pyrazinamine (8) (neat POBr3, open vessel, 145°C, 20 min 40%) 1012 3-bromo-2-pyrazinamine was made similarly.1008 Also other examples.80,86 295 825,956 1033 1290 1386 1396 

5-(Furan-2-yl)-2(l/7)-pyrazinone gave 2-chloro-5-(furan-2-yl)pyrazine (3) (POCI3, 

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