Chlorination sulfuryl chloride, pyrazine

Sufficient activation was present in 5-ethylamino-2-oxoimidazolo [4,5-6]pyrazine (173) for it to be halogenated in the 6-position by chlorine and bromine in acetic acid or by sulfuryl chloride (69FRP1578366 71BRP1248146). The 2-oxo group could be replaced by chlorine (75KFZ10 76KFZ35). 

Taft reported the conversion of chloropyrazine into 2,6-dichloro-pyrazine by chlorination with sulfuryl chloride or liquid chlorine.274 This reaction is conveniently carried out in the laboratory by heating 2-chloropyrazine and sulfuryl chloride in a sealed tube at 120° for 3 hours. More recently 2,6-dichloropyrazine has been prepared in 90% yield from chloropyrazine by reaction with chlorine in dimethyl-formamide at 70°-75° 2,3-dichloropyrazine is obtained in 84% yield... 

Various imidazo[4,5-fc]pyrazin-2-ones (228) have been subjected to a number of different reactions. Alkylation, acylation and the Mannich reaction all give 1,3-disubstituted derivatives (229). Halogenation of the 2-oxo compound (230) with bromine or chlorine in acetic acid or with sulfuryl chloride provided monohalo derivatives (231) (69FRP1578366, 71BRP1248146). The chlorine atom of (231) can be removed by catalytic hydrogenation. 

A series of monoalkylpyrazines has been chlorinated specifically at the 3-position with sulfuryl chloride in the presence of iV,V-dimethylformamide the nucleus of 2,6-dialkylpyrazines is also readily chlorinated (687,693). The reaction of isobutyl-pyrazine with phosphoryl chloride and phosphorus pentachloride gave 2-chloro-5-isobutylpyrazine in 25% yield (693). 2-Acetonylpyrazine and 2-phenacylpyrazine with aqueous potassium hypochlorite gave 2-dichloromethylpyrazine (694). 

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