2 -pyrazinone with thionyl chloride

Diphenyl-3-nitro-2-pyrazinone (85) undergoes displacement of the nitro group (cf. Section II,D,2,c) by halide ion in aqueous acid (protonation of the 0x0 oxygen atom), with thionyl chloride (formation of —0—SO—Cl which in this case does not go to chloro), and with phosphorus oxychloride [formation of —0— POCl2 (86) which goes to chloro, but more slowly than nitro displacement occurs]. 

Treatment of 2(l//)-pyrazinone (63) with thionyl chloride and triethylamine appears to give both 2-oxo-l, 2-dihydro-l -pyrazinesulfinyl chloride (64) and 5-oxo-... 

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